aver/codegen/lean/

mod.rs

/// Lean 4 backend for the Aver transpiler.
///
/// Transpiles only pure core logic: functions without effects, type definitions,
/// verify blocks (as `example` proofs), and decision blocks (as comments).
/// Effectful functions and `main` are skipped.
mod builtins;
mod expr;
mod law_auto;
mod pattern;
mod recurrence;
mod shared;
mod toplevel;
mod types;

use std::collections::{HashMap, HashSet};

use crate::ast::{
    BinOp, Expr, FnBody, FnDef, MatchArm, Pattern, Stmt, TopLevel, TypeDef, VerifyKind,
};
use crate::call_graph;
use crate::codegen::{CodegenContext, ProjectOutput};

/// How verify blocks should be emitted in generated Lean.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum VerifyEmitMode {
    /// `example : lhs = rhs := by native_decide`
    NativeDecide,
    /// `example : lhs = rhs := by sorry`
    Sorry,
    /// Named theorem stubs:
    /// `theorem <fn>_verify_<n> : lhs = rhs := by`
    /// `  sorry`
    TheoremSkeleton,
}

/// Proof-mode recursion support class for emitted Lean definitions.
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum RecursionPlan {
    /// Single-function recursion where an `Int` parameter decreases by 1.
    IntCountdown { param_index: usize },
    /// Single-function recursion where an `Int` parameter increases by 1 up to a bound.
    /// `bound_lean` is the Lean expression of the upper bound (e.g. `8` or `xs.length`).
    IntAscending {
        param_index: usize,
        bound_lean: String,
    },
    /// Single-function recurrence with `n < 0` guard, `0/1` bases, and a linear
    /// second-order recurrence over previous results, emitted through a private
    /// Nat helper.
    LinearRecurrence2,
    /// Single-function structural recursion on a `List<_>` parameter.
    ListStructural { param_index: usize },
    /// Single-function structural recursion on a recursive user-defined type parameter.
    SizeOfStructural,
    /// Single-function recursion where first `String` stays the same and second `Int`
    /// parameter strictly advances (`pos + k`, `k >= 1`).
    StringPosAdvance,
    /// Mutual recursion group where first `Int` parameter decreases by 1 across SCC calls.
    MutualIntCountdown,
    /// Mutual recursion group where first `String` is preserved and second `Int`
    /// either stays the same across rank-decreasing edges, or strictly advances.
    MutualStringPosAdvance { rank: usize },
    /// Generic mutual recursion plan using `sizeOf` on structural parameters,
    /// plus rank for same-measure edges.
    MutualSizeOfRanked { rank: usize },
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct ProofModeIssue {
    pub line: usize,
    pub message: String,
}

const LEAN_PRELUDE_HEADER: &str = r#"-- Generated by the Aver → Lean 4 transpiler
-- Pure core logic only (effectful functions are omitted)

set_option linter.unusedVariables false

-- Prelude: helper definitions for Aver builtins"#;

const LEAN_PRELUDE_FLOAT_COE: &str = r#"instance : Coe Int Float := ⟨fun n => Float.ofInt n⟩

def Float.fromInt (n : Int) : Float := Float.ofInt n"#;

const LEAN_PRELUDE_FLOAT_DEC_EQ: &str = r#"private unsafe def Float.unsafeDecEq (a b : Float) : Decidable (a = b) :=
  if a == b then isTrue (unsafeCast ()) else isFalse (unsafeCast ())
@[implemented_by Float.unsafeDecEq]
private opaque Float.compDecEq (a b : Float) : Decidable (a = b)
instance : DecidableEq Float := Float.compDecEq"#;

const LEAN_PRELUDE_EXCEPT_DEC_EQ: &str = r#"instance [DecidableEq ε] [DecidableEq α] : DecidableEq (Except ε α)
  | .ok a, .ok b =>
    if h : a = b then isTrue (h ▸ rfl) else isFalse (by intro h'; cases h'; exact h rfl)
  | .error a, .error b =>
    if h : a = b then isTrue (h ▸ rfl) else isFalse (by intro h'; cases h'; exact h rfl)
  | .ok _, .error _ => isFalse (by intro h; cases h)
  | .error _, .ok _ => isFalse (by intro h; cases h)"#;

const LEAN_PRELUDE_EXCEPT_NS: &str = r#"namespace Except
def withDefault (r : Except ε α) (d : α) : α :=
  match r with
  | .ok v => v
  | .error _ => d
end Except"#;

const LEAN_PRELUDE_OPTION_TO_EXCEPT: &str = r#"def Option.toExcept (o : Option α) (e : ε) : Except ε α :=
  match o with
  | some v => .ok v
  | none => .error e"#;

const LEAN_PRELUDE_STRING_HADD: &str = r#"instance : HAdd String String String := ⟨String.append⟩"#;

const LEAN_PRELUDE_PROOF_FUEL: &str = r#"def averStringPosFuel (s : String) (pos : Int) (rankBudget : Nat) : Nat :=
  (((s.data.length) - pos.toNat) + 1) * rankBudget"#;

const LEAN_PRELUDE_AVER_MEASURE: &str = r#"namespace AverMeasure
def list (elemMeasure : α → Nat) : List α → Nat
  | [] => 1
  | x :: xs => elemMeasure x + list elemMeasure xs + 1
def option (elemMeasure : α → Nat) : Option α → Nat
  | none => 1
  | some x => elemMeasure x + 1
def except (errMeasure : ε → Nat) (okMeasure : α → Nat) : Except ε α → Nat
  | .error e => errMeasure e + 1
  | .ok v => okMeasure v + 1
end AverMeasure"#;

const AVER_MAP_PRELUDE_BASE: &str = r#"namespace AverMap
def empty : List (α × β) := []
def get [DecidableEq α] (m : List (α × β)) (k : α) : Option β :=
  match m with
  | [] => none
  | (k', v) :: rest => if k = k' then some v else AverMap.get rest k
def set [DecidableEq α] (m : List (α × β)) (k : α) (v : β) : List (α × β) :=
  let rec go : List (α × β) → List (α × β)
    | [] => [(k, v)]
    | (k', v') :: rest => if k = k' then (k, v) :: rest else (k', v') :: go rest
  go m
def has [DecidableEq α] (m : List (α × β)) (k : α) : Bool :=
  m.any (fun p => decide (k = p.1))
def remove [DecidableEq α] (m : List (α × β)) (k : α) : List (α × β) :=
  m.filter (fun p => !(decide (k = p.1)))
def keys (m : List (α × β)) : List α := m.map Prod.fst
def values (m : List (α × β)) : List β := m.map Prod.snd
def entries (m : List (α × β)) : List (α × β) := m
def len (m : List (α × β)) : Nat := m.length
def fromList (entries : List (α × β)) : List (α × β) := entries"#;

const AVER_MAP_PRELUDE_HAS_SET_SELF: &str = r#"private theorem any_set_go_self [DecidableEq α] (k : α) (v : β) :
    ∀ (m : List (α × β)), List.any (AverMap.set.go k v m) (fun p => decide (k = p.1)) = true := by
  intro m
  induction m with
  | nil =>
      simp [AverMap.set.go, List.any]
  | cons p tl ih =>
      cases p with
      | mk k' v' =>
          by_cases h : k = k'
          · simp [AverMap.set.go, List.any, h]
          · simp [AverMap.set.go, List.any, h, ih]

theorem has_set_self [DecidableEq α] (m : List (α × β)) (k : α) (v : β) :
    AverMap.has (AverMap.set m k v) k = true := by
  simpa [AverMap.has, AverMap.set] using any_set_go_self k v m"#;

const AVER_MAP_PRELUDE_GET_SET_SELF: &str = r#"private theorem get_set_go_self [DecidableEq α] (k : α) (v : β) :
    ∀ (m : List (α × β)), AverMap.get (AverMap.set.go k v m) k = some v := by
  intro m
  induction m with
  | nil =>
      simp [AverMap.set.go, AverMap.get]
  | cons p tl ih =>
      cases p with
      | mk k' v' =>
          by_cases h : k = k'
          · simp [AverMap.set.go, AverMap.get, h]
          · simp [AverMap.set.go, AverMap.get, h, ih]

theorem get_set_self [DecidableEq α] (m : List (α × β)) (k : α) (v : β) :
    AverMap.get (AverMap.set m k v) k = some v := by
  simpa [AverMap.set] using get_set_go_self k v m"#;

const AVER_MAP_PRELUDE_GET_SET_OTHER: &str = r#"private theorem get_set_go_other [DecidableEq α] (k key : α) (v : β) (h : key ≠ k) :
    ∀ (m : List (α × β)), AverMap.get (AverMap.set.go k v m) key = AverMap.get m key := by
  intro m
  induction m with
  | nil =>
      simp [AverMap.set.go, AverMap.get, h]
  | cons p tl ih =>
      cases p with
      | mk k' v' =>
          by_cases hk : k = k'
          · have hkey : key ≠ k' := by simpa [hk] using h
            simp [AverMap.set.go, AverMap.get, hk, hkey]
          · by_cases hkey : key = k'
            · simp [AverMap.set.go, AverMap.get, hk, hkey]
            · simp [AverMap.set.go, AverMap.get, hk, hkey, ih]

theorem get_set_other [DecidableEq α] (m : List (α × β)) (k key : α) (v : β) (h : key ≠ k) :
    AverMap.get (AverMap.set m k v) key = AverMap.get m key := by
  simpa [AverMap.set] using get_set_go_other k key v h m"#;

const AVER_MAP_PRELUDE_HAS_SET_OTHER: &str = r#"theorem has_eq_isSome_get [DecidableEq α] (m : List (α × β)) (k : α) :
    AverMap.has m k = (AverMap.get m k).isSome := by
  induction m with
  | nil =>
      simp [AverMap.has, AverMap.get]
  | cons p tl ih =>
      cases p with
      | mk k' v' =>
          by_cases h : k = k'
          · simp [AverMap.has, AverMap.get, List.any, h]
          · simpa [AverMap.has, AverMap.get, List.any, h] using ih

theorem has_set_other [DecidableEq α] (m : List (α × β)) (k key : α) (v : β) (h : key ≠ k) :
    AverMap.has (AverMap.set m k v) key = AverMap.has m key := by
  rw [AverMap.has_eq_isSome_get, AverMap.has_eq_isSome_get]
  simp [AverMap.get_set_other, h]"#;

const AVER_MAP_PRELUDE_END: &str = r#"end AverMap"#;

const LEAN_PRELUDE_AVER_LIST: &str = r#"namespace AverList
def get (xs : List α) (i : Int) : Option α :=
  if i < 0 then none else xs.get? i.toNat
private def insertSorted [Ord α] (x : α) : List α → List α
  | [] => [x]
  | y :: ys =>
    if compare x y == Ordering.lt || compare x y == Ordering.eq then
      x :: y :: ys
    else
      y :: insertSorted x ys
def sort [Ord α] (xs : List α) : List α :=
  xs.foldl (fun acc x => insertSorted x acc) []
end AverList"#;

const LEAN_PRELUDE_HEADER_TYPE: &str = r#"structure Header where
  name : String
  value : String
  deriving Repr, BEq, Inhabited, DecidableEq"#;

const LEAN_PRELUDE_HTTP_RESPONSE_TYPE: &str = r#"structure HttpResponse where
  status : Int
  body : String
  headers : List Header
  deriving Repr, BEq, Inhabited, DecidableEq"#;

const LEAN_PRELUDE_HTTP_REQUEST_TYPE: &str = r#"structure HttpRequest where
  method : String
  path : String
  body : String
  headers : List Header
  deriving Repr, BEq, Inhabited, DecidableEq"#;

const LEAN_PRELUDE_TCP_CONNECTION_TYPE: &str = r#"structure Tcp_Connection where
  id : String
  host : String
  port : Int
  deriving Repr, BEq, Inhabited, DecidableEq"#;

const LEAN_PRELUDE_STRING_HELPERS: &str = r#"def String.charAt (s : String) (i : Int) : Option String :=
  if i < 0 then none
  else (s.toList.get? i.toNat).map Char.toString
theorem String.charAt_length_none (s : String) : String.charAt s s.length = none := by
  have hs : ¬ ((s.length : Int) < 0) := by omega
  unfold String.charAt
  simp [hs]
  change s.data.length ≤ s.length
  exact Nat.le_refl _
def String.slice (s : String) (start stop : Int) : String :=
  let startN := if start < 0 then 0 else start.toNat
  let stopN := if stop < 0 then 0 else stop.toNat
  let chars := s.toList
  String.mk ((chars.drop startN).take (stopN - startN))
private def trimFloatTrailingZerosChars (chars : List Char) : List Char :=
  let noZeros := (chars.reverse.dropWhile (fun c => c == '0')).reverse
  match noZeros.reverse with
  | '.' :: rest => rest.reverse
  | _ => noZeros
private def normalizeFloatString (s : String) : String :=
  if s.toList.any (fun c => c == '.') then
    String.mk (trimFloatTrailingZerosChars s.toList)
  else s
def String.fromFloat (f : Float) : String := normalizeFloatString (toString f)
def String.chars (s : String) : List String := s.toList.map Char.toString
private theorem char_to_string_append_mk (c : Char) (chars : List Char) :
    Char.toString c ++ String.mk chars = String.mk (c :: chars) := by
  rfl
private theorem string_intercalate_empty_char_strings_go (acc : String) (chars : List Char) :
    String.intercalate.go acc "" (chars.map Char.toString) = acc ++ String.mk chars := by
  induction chars generalizing acc with
  | nil =>
      simp [String.intercalate.go]
  | cons c rest ih =>
      calc
        String.intercalate.go acc "" ((c :: rest).map Char.toString)
            = String.intercalate.go (acc ++ Char.toString c) "" (rest.map Char.toString) := by
                simp [String.intercalate.go]
        _ = (acc ++ Char.toString c) ++ String.mk rest := by
                simpa using ih (acc ++ Char.toString c)
        _ = acc ++ String.mk (c :: rest) := by
                simp [String.append_assoc, char_to_string_append_mk]
private theorem string_intercalate_empty_char_strings (chars : List Char) :
    String.intercalate "" (chars.map Char.toString) = String.mk chars := by
  cases chars with
  | nil =>
      simp [String.intercalate]
  | cons c rest =>
      simpa [String.intercalate] using string_intercalate_empty_char_strings_go c.toString rest
theorem String.intercalate_empty_chars (s : String) :
    String.intercalate "" (String.chars s) = s := by
  cases s with
  | mk chars =>
      simpa [String.chars] using string_intercalate_empty_char_strings chars
namespace AverString
def splitOnCharGo (currentRev : List Char) (sep : Char) : List Char → List String
  | [] => [String.mk currentRev.reverse]
  | c :: cs =>
      if c == sep then
        String.mk currentRev.reverse :: splitOnCharGo [] sep cs
      else
        splitOnCharGo (c :: currentRev) sep cs
def splitOnChar (s : String) (sep : Char) : List String :=
  splitOnCharGo [] sep s.toList
def split (s delim : String) : List String :=
  match delim.toList with
  | [] => "" :: (s.toList.map Char.toString) ++ [""]
  | [c] => splitOnChar s c
  | _ => s.splitOn delim
@[simp] private theorem char_toString_data (c : Char) : c.toString.data = [c] := by
  rfl
private theorem splitOnCharGo_until_sep
    (prefixRev part tail : List Char) (sep : Char) :
    part.all (fun c => c != sep) = true ->
    splitOnCharGo prefixRev sep (part ++ sep :: tail) =
      String.mk (prefixRev.reverse ++ part) :: splitOnCharGo [] sep tail := by
  intro h_safe
  induction part generalizing prefixRev with
  | nil =>
      simp [splitOnCharGo]
  | cons c rest ih =>
      simp at h_safe
      have h_rest : (rest.all fun c => c != sep) = true := by
        simpa using h_safe.2
      simpa [splitOnCharGo, h_safe.1, List.reverse_cons, List.append_assoc] using
        (ih (c :: prefixRev) h_rest)
private theorem splitOnCharGo_no_sep
    (prefixRev chars : List Char) (sep : Char) :
    chars.all (fun c => c != sep) = true ->
    splitOnCharGo prefixRev sep chars =
      [String.mk (prefixRev.reverse ++ chars)] := by
  intro h_safe
  induction chars generalizing prefixRev with
  | nil =>
      simp [splitOnCharGo]
  | cons c rest ih =>
      simp at h_safe
      have h_rest : (rest.all fun c => c != sep) = true := by
        simpa using h_safe.2
      simpa [splitOnCharGo, h_safe.1, List.reverse_cons, List.append_assoc] using
        (ih (c :: prefixRev) h_rest)
@[simp] theorem split_single_char_append
    (head tail : String) (sep : Char) :
    head.toList.all (fun c => c != sep) = true ->
    split (head ++ Char.toString sep ++ tail) (Char.toString sep) =
      head :: split tail (Char.toString sep) := by
  intro h_safe
  simpa [split, splitOnChar] using
    (splitOnCharGo_until_sep [] head.data tail.data sep h_safe)
@[simp] theorem split_single_char_no_sep
    (s : String) (sep : Char) :
    s.toList.all (fun c => c != sep) = true ->
    split s (Char.toString sep) = [s] := by
  intro h_safe
  simpa [split, splitOnChar] using
    (splitOnCharGo_no_sep [] s.data sep h_safe)
private theorem intercalate_go_prefix
    (pref acc sep : String) (rest : List String) :
    String.intercalate.go (pref ++ sep ++ acc) sep rest =
      pref ++ sep ++ String.intercalate.go acc sep rest := by
  induction rest generalizing acc with
  | nil =>
      simp [String.intercalate.go, String.append_assoc]
  | cons x xs ih =>
      simpa [String.intercalate.go, String.append_assoc] using
        (ih (acc ++ sep ++ x))
@[simp] theorem split_intercalate_trailing_single_char
    (parts : List String) (sep : Char) :
    parts.all (fun part => part.toList.all (fun c => c != sep)) = true ->
    split (String.intercalate (Char.toString sep) parts ++ Char.toString sep) (Char.toString sep) =
      match parts with
      | [] => ["", ""]
      | _ => parts ++ [""] := by
  intro h_safe
  induction parts with
  | nil =>
      simp [split, splitOnChar, splitOnCharGo]
  | cons part rest ih =>
      simp at h_safe
      have h_part : (part.toList.all fun c => c != sep) = true := by
        simpa using h_safe.1
      cases rest with
      | nil =>
          have h_empty : ("".toList.all fun c => c != sep) = true := by simp
          calc
            split (String.intercalate.go part (Char.toString sep) [] ++ Char.toString sep) (Char.toString sep)
                = split (part ++ Char.toString sep) (Char.toString sep) := by
                    simp [String.intercalate.go]
            _ = part :: split "" (Char.toString sep) := by
                    simpa using split_single_char_append part "" sep h_part
            _ = [part, ""] := by
                    simp [split_single_char_no_sep, h_empty]
      | cons next rest' =>
          have h_rest : ((next :: rest').all fun part => part.toList.all fun c => c != sep) = true := by
            simpa using h_safe.2
          calc
            split
                  (String.intercalate.go part (Char.toString sep) (next :: rest') ++ Char.toString sep)
                  (Char.toString sep)
                =
                  split
                    (part ++ Char.toString sep ++ (String.intercalate (Char.toString sep) (next :: rest') ++ Char.toString sep))
                    (Char.toString sep) := by
                    have h_join :
                        String.intercalate.go part (Char.toString sep) (next :: rest') ++ Char.toString sep
                          = part ++ Char.toString sep ++ (String.intercalate (Char.toString sep) (next :: rest') ++ Char.toString sep) := by
                        calc
                          String.intercalate.go part (Char.toString sep) (next :: rest') ++ Char.toString sep
                              = String.intercalate.go (part ++ Char.toString sep ++ next) (Char.toString sep) rest' ++ Char.toString sep := by
                                  simp [String.intercalate.go]
                          _ = part ++ Char.toString sep ++ (String.intercalate.go next (Char.toString sep) rest' ++ Char.toString sep) := by
                                  rw [intercalate_go_prefix part next (Char.toString sep) rest']
                                  simp [String.append_assoc]
                          _ = part ++ Char.toString sep ++ (String.intercalate (Char.toString sep) (next :: rest') ++ Char.toString sep) := by
                                  simp [String.intercalate, String.intercalate.go]
                    simpa using congrArg (fun s => split s (Char.toString sep)) h_join
            _ = part :: split
                    (String.intercalate (Char.toString sep) (next :: rest') ++ Char.toString sep)
                    (Char.toString sep) := by
                    simpa using split_single_char_append
                      part
                      (String.intercalate (Char.toString sep) (next :: rest') ++ Char.toString sep)
                      sep
                      h_part
            _ = part :: (next :: rest' ++ [""]) := by
                    simpa using ih h_rest
end AverString"#;

const LEAN_PRELUDE_NUMERIC_PARSE: &str = r#"namespace AverDigits
def foldDigitsAcc (acc : Nat) : List Nat -> Nat
  | [] => acc
  | d :: ds => foldDigitsAcc (acc * 10 + d) ds

def foldDigits (digits : List Nat) : Nat :=
  foldDigitsAcc 0 digits

private theorem foldDigitsAcc_append_singleton (acc : Nat) (xs : List Nat) (d : Nat) :
    foldDigitsAcc acc (xs ++ [d]) = foldDigitsAcc acc xs * 10 + d := by
  induction xs generalizing acc with
  | nil =>
      simp [foldDigitsAcc]
  | cons x xs ih =>
      simp [foldDigitsAcc, ih, Nat.left_distrib, Nat.add_assoc, Nat.add_left_comm]

private theorem foldDigits_append_singleton (xs : List Nat) (d : Nat) :
    foldDigits (xs ++ [d]) = foldDigits xs * 10 + d := by
  simpa [foldDigits] using foldDigitsAcc_append_singleton 0 xs d

def natDigits : Nat -> List Nat
  | n =>
      if n < 10 then
        [n]
      else
        natDigits (n / 10) ++ [n % 10]
termination_by
  n => n

theorem natDigits_nonempty (n : Nat) : natDigits n ≠ [] := by
  by_cases h : n < 10
  · rw [natDigits.eq_1]
    simp [h]
  · rw [natDigits.eq_1]
    simp [h]

theorem natDigits_digits_lt_ten : ∀ n : Nat, ∀ d ∈ natDigits n, d < 10 := by
  intro n d hd
  by_cases h : n < 10
  · rw [natDigits.eq_1] at hd
    simp [h] at hd
    rcases hd with rfl
    exact h
  · rw [natDigits.eq_1] at hd
    simp [h] at hd
    rcases hd with hd | hd
    · exact natDigits_digits_lt_ten (n / 10) d hd
    · subst hd
      exact Nat.mod_lt n (by omega)

theorem foldDigits_natDigits : ∀ n : Nat, foldDigits (natDigits n) = n := by
  intro n
  by_cases h : n < 10
  · rw [natDigits.eq_1]
    simp [h, foldDigits, foldDigitsAcc]
  · rw [natDigits.eq_1]
    simp [h]
    rw [foldDigits_append_singleton]
    rw [foldDigits_natDigits (n / 10)]
    omega

def digitChar : Nat -> Char
  | 0 => '0' | 1 => '1' | 2 => '2' | 3 => '3' | 4 => '4'
  | 5 => '5' | 6 => '6' | 7 => '7' | 8 => '8' | 9 => '9'
  | _ => '0'

def charToDigit? : Char -> Option Nat
  | '0' => some 0 | '1' => some 1 | '2' => some 2 | '3' => some 3 | '4' => some 4
  | '5' => some 5 | '6' => some 6 | '7' => some 7 | '8' => some 8 | '9' => some 9
  | _ => none

theorem charToDigit_digitChar : ∀ d : Nat, d < 10 -> charToDigit? (digitChar d) = some d
  | 0, _ => by simp [digitChar, charToDigit?]
  | 1, _ => by simp [digitChar, charToDigit?]
  | 2, _ => by simp [digitChar, charToDigit?]
  | 3, _ => by simp [digitChar, charToDigit?]
  | 4, _ => by simp [digitChar, charToDigit?]
  | 5, _ => by simp [digitChar, charToDigit?]
  | 6, _ => by simp [digitChar, charToDigit?]
  | 7, _ => by simp [digitChar, charToDigit?]
  | 8, _ => by simp [digitChar, charToDigit?]
  | 9, _ => by simp [digitChar, charToDigit?]
  | Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ n))))))))), h => by
      omega

theorem digitChar_ne_minus : ∀ d : Nat, d < 10 -> digitChar d ≠ '-'
  | 0, _ => by decide
  | 1, _ => by decide
  | 2, _ => by decide
  | 3, _ => by decide
  | 4, _ => by decide
  | 5, _ => by decide
  | 6, _ => by decide
  | 7, _ => by decide
  | 8, _ => by decide
  | 9, _ => by decide
  | Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ n))))))))), h => by
      omega

theorem digitChar_not_ws : ∀ d : Nat, d < 10 ->
    Char.toString (digitChar d) ≠ " " ∧
    Char.toString (digitChar d) ≠ "\t" ∧
    Char.toString (digitChar d) ≠ "\n" ∧
    Char.toString (digitChar d) ≠ "\r"
  | 0, _ => by decide
  | 1, _ => by decide
  | 2, _ => by decide
  | 3, _ => by decide
  | 4, _ => by decide
  | 5, _ => by decide
  | 6, _ => by decide
  | 7, _ => by decide
  | 8, _ => by decide
  | 9, _ => by decide
  | Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ (Nat.succ n))))))))), h => by
      omega

theorem mapM_charToDigit_digits : ∀ ds : List Nat,
    (∀ d ∈ ds, d < 10) -> List.mapM charToDigit? (ds.map digitChar) = some ds := by
  intro ds hds
  induction ds with
  | nil =>
      simp
  | cons d ds ih =>
      have hd : d < 10 := hds d (by simp)
      have htail : ∀ x ∈ ds, x < 10 := by
        intro x hx
        exact hds x (by simp [hx])
      simp [charToDigit_digitChar d hd, ih htail]

def natDigitsChars (n : Nat) : List Char :=
  (natDigits n).map digitChar

def parseNatChars (chars : List Char) : Option Nat :=
  match chars with
  | [] => none
  | _ => do
      let digits <- List.mapM charToDigit? chars
      pure (foldDigits digits)

theorem parseNatChars_nat (n : Nat) :
    parseNatChars (natDigitsChars n) = some n := by
  unfold parseNatChars natDigitsChars
  cases h : (natDigits n).map digitChar with
  | nil =>
      exfalso
      exact natDigits_nonempty n (List.map_eq_nil_iff.mp h)
  | cons hd tl =>
      have hdigits : List.mapM charToDigit? (List.map digitChar (natDigits n)) = some (natDigits n) :=
        mapM_charToDigit_digits (natDigits n) (fun d hd => natDigits_digits_lt_ten n d hd)
      rw [h] at hdigits
      simp [h, hdigits, foldDigits_natDigits]
end AverDigits

def String.fromInt (n : Int) : String :=
  match n with
  | .ofNat m => String.mk (AverDigits.natDigitsChars m)
  | .negSucc m => String.mk ('-' :: AverDigits.natDigitsChars (m + 1))

def Int.fromString (s : String) : Except String Int :=
  match s.toList with
  | [] => .error ("Cannot parse '" ++ s ++ "' as Int")
  | '-' :: rest =>
    match AverDigits.parseNatChars rest with
    | some n => .ok (-Int.ofNat n)
    | none => .error ("Cannot parse '" ++ s ++ "' as Int")
  | chars =>
    match AverDigits.parseNatChars chars with
    | some n => .ok (Int.ofNat n)
    | none => .error ("Cannot parse '" ++ s ++ "' as Int")

theorem Int.fromString_fromInt : ∀ n : Int, Int.fromString (String.fromInt n) = .ok n
  | .ofNat m => by
      cases h : AverDigits.natDigits m with
      | nil =>
          exfalso
          exact AverDigits.natDigits_nonempty m h
      | cons d ds =>
          have hd : d < 10 := AverDigits.natDigits_digits_lt_ten m d (by simp [h])
          have hne : AverDigits.digitChar d ≠ '-' := AverDigits.digitChar_ne_minus d hd
          have hparse : AverDigits.parseNatChars (AverDigits.digitChar d :: List.map AverDigits.digitChar ds) = some m := by
            simpa [AverDigits.natDigitsChars, h] using AverDigits.parseNatChars_nat m
          simp [String.fromInt, Int.fromString, AverDigits.natDigitsChars, h, hne, hparse]
  | .negSucc m => by
      simp [String.fromInt, Int.fromString, AverDigits.parseNatChars_nat]
      rfl

private def charDigitsToNat (cs : List Char) : Nat :=
  cs.foldl (fun acc c => acc * 10 + (c.toNat - '0'.toNat)) 0

private def parseExpPart : List Char → (Bool × List Char)
  | '-' :: rest => (true, rest.takeWhile Char.isDigit)
  | '+' :: rest => (false, rest.takeWhile Char.isDigit)
  | rest => (false, rest.takeWhile Char.isDigit)

def Float.fromString (s : String) : Except String Float :=
  let chars := s.toList
  let (neg, chars) := match chars with
    | '-' :: rest => (true, rest)
    | _ => (false, chars)
  let intPart := chars.takeWhile Char.isDigit
  let rest := chars.dropWhile Char.isDigit
  let (fracPart, rest) := match rest with
    | '.' :: rest => (rest.takeWhile Char.isDigit, rest.dropWhile Char.isDigit)
    | _ => ([], rest)
  let (expNeg, expDigits) := match rest with
    | 'e' :: rest => parseExpPart rest
    | 'E' :: rest => parseExpPart rest
    | _ => (false, [])
  if intPart.isEmpty && fracPart.isEmpty then .error ("Invalid float: " ++ s)
  else
    let mantissa := charDigitsToNat (intPart ++ fracPart)
    let fracLen : Int := fracPart.length
    let expVal : Int := charDigitsToNat expDigits
    let shift : Int := (if expNeg then -expVal else expVal) - fracLen
    let f := if shift >= 0 then Float.ofScientific mantissa false shift.toNat
             else Float.ofScientific mantissa true ((-shift).toNat)
    .ok (if neg then -f else f)"#;

const LEAN_PRELUDE_CHAR_BYTE: &str = r#"def Char.toCode (s : String) : Int :=
  match s.toList.head? with
  | some c => (c.toNat : Int)
  | none => panic! "Char.toCode: string is empty"
def Char.fromCode (n : Int) : Option String :=
  if n < 0 || n > 1114111 then none
  else if n >= 55296 && n <= 57343 then none
  else some (Char.toString (Char.ofNat n.toNat))

def hexDigit (n : Int) : String :=
  match n with
  | 0 => "0" | 1 => "1" | 2 => "2" | 3 => "3"
  | 4 => "4" | 5 => "5" | 6 => "6" | 7 => "7"
  | 8 => "8" | 9 => "9" | 10 => "a" | 11 => "b"
  | 12 => "c" | 13 => "d" | 14 => "e" | 15 => "f"
  | _ => "?"

def byteToHex (code : Int) : String :=
  hexDigit (code / 16) ++ hexDigit (code % 16)

namespace AverByte
private def hexValue (c : Char) : Option Int :=
  match c with
  | '0' => some 0  | '1' => some 1  | '2' => some 2  | '3' => some 3
  | '4' => some 4  | '5' => some 5  | '6' => some 6  | '7' => some 7
  | '8' => some 8  | '9' => some 9  | 'a' => some 10 | 'b' => some 11
  | 'c' => some 12 | 'd' => some 13 | 'e' => some 14 | 'f' => some 15
  | 'A' => some 10 | 'B' => some 11 | 'C' => some 12 | 'D' => some 13
  | 'E' => some 14 | 'F' => some 15
  | _ => none
def toHex (n : Int) : Except String String :=
  if n < 0 || n > 255 then
    .error ("Byte.toHex: " ++ toString n ++ " is out of range 0-255")
  else
    .ok (byteToHex n)
def fromHex (s : String) : Except String Int :=
  match s.toList with
  | [hi, lo] =>
    match hexValue hi, hexValue lo with
    | some h, some l => .ok (h * 16 + l)
    | _, _ => .error ("Byte.fromHex: invalid hex '" ++ s ++ "'")
  | _ => .error ("Byte.fromHex: expected exactly 2 hex chars, got '" ++ s ++ "'")
end AverByte"#;

fn pure_fns(ctx: &CodegenContext) -> Vec<&FnDef> {
    ctx.modules
        .iter()
        .flat_map(|m| m.fn_defs.iter())
        .chain(ctx.fn_defs.iter())
        .filter(|fd| toplevel::is_pure_fn(fd))
        .collect()
}

fn recursive_type_names(ctx: &CodegenContext) -> HashSet<String> {
    ctx.modules
        .iter()
        .flat_map(|m| m.type_defs.iter())
        .chain(ctx.type_defs.iter())
        .filter(|td| toplevel::is_recursive_type_def(td))
        .map(|td| toplevel::type_def_name(td).to_string())
        .collect()
}

fn recursive_pure_fn_names(ctx: &CodegenContext) -> HashSet<String> {
    let pure_names: HashSet<String> = pure_fns(ctx)
        .into_iter()
        .map(|fd| fd.name.clone())
        .collect();
    let mut callgraph_items = ctx.items.clone();
    for module in &ctx.modules {
        for fd in &module.fn_defs {
            callgraph_items.push(TopLevel::FnDef(fd.clone()));
        }
    }
    call_graph::find_recursive_fns(&callgraph_items)
        .into_iter()
        .filter(|name| pure_names.contains(name))
        .collect()
}

fn verify_counter_key(vb: &crate::ast::VerifyBlock) -> String {
    match &vb.kind {
        VerifyKind::Cases => format!("fn:{}", vb.fn_name),
        VerifyKind::Law(law) => format!("law:{}::{}", vb.fn_name, law.name),
    }
}

fn lean_project_name(ctx: &CodegenContext) -> String {
    ctx.items
        .iter()
        .find_map(|item| match item {
            TopLevel::Module(m) => Some(m.name.clone()),
            _ => None,
        })
        .unwrap_or_else(|| capitalize_first(&ctx.project_name))
}

fn expr_to_dotted_name(expr: &Expr) -> Option<String> {
    match expr {
        Expr::Ident(name) => Some(name.clone()),
        Expr::Attr(obj, field) => expr_to_dotted_name(obj).map(|p| format!("{}.{}", p, field)),
        _ => None,
    }
}

fn call_matches(name: &str, target: &str) -> bool {
    name == target || name.rsplit('.').next() == Some(target)
}

fn call_is_in_set(name: &str, targets: &HashSet<String>) -> bool {
    call_matches_any(name, targets)
}

fn canonical_callee_name(name: &str, targets: &HashSet<String>) -> Option<String> {
    if targets.contains(name) {
        return Some(name.to_string());
    }
    name.rsplit('.')
        .next()
        .filter(|last| targets.contains(*last))
        .map(ToString::to_string)
}

fn call_matches_any(name: &str, targets: &HashSet<String>) -> bool {
    if targets.contains(name) {
        return true;
    }
    match name.rsplit('.').next() {
        Some(last) => targets.contains(last),
        None => false,
    }
}

fn is_int_minus_positive(expr: &Expr, param_name: &str) -> bool {
    match expr {
        Expr::BinOp(BinOp::Sub, left, right) => {
            matches!(left.as_ref(), Expr::Ident(id) if id == param_name)
                && matches!(right.as_ref(), Expr::Literal(crate::ast::Literal::Int(n)) if *n >= 1)
        }
        Expr::FnCall(callee, args) => {
            let Some(name) = expr_to_dotted_name(callee) else {
                return false;
            };
            (name == "Int.sub" || name == "int.sub")
                && args.len() == 2
                && matches!(&args[0], Expr::Ident(id) if id == param_name)
                && matches!(&args[1], Expr::Literal(crate::ast::Literal::Int(n)) if *n >= 1)
        }
        _ => false,
    }
}

fn collect_calls_from_expr<'a>(expr: &'a Expr, out: &mut Vec<(String, Vec<&'a Expr>)>) {
    match expr {
        Expr::FnCall(callee, args) => {
            if let Some(name) = expr_to_dotted_name(callee) {
                out.push((name, args.iter().collect()));
            }
            collect_calls_from_expr(callee, out);
            for arg in args {
                collect_calls_from_expr(arg, out);
            }
        }
        Expr::TailCall(boxed) => {
            let (name, args) = boxed.as_ref();
            out.push((name.clone(), args.iter().collect()));
            for arg in args {
                collect_calls_from_expr(arg, out);
            }
        }
        Expr::Attr(obj, _) => collect_calls_from_expr(obj, out),
        Expr::BinOp(_, left, right) => {
            collect_calls_from_expr(left, out);
            collect_calls_from_expr(right, out);
        }
        Expr::Match { subject, arms, .. } => {
            collect_calls_from_expr(subject, out);
            for arm in arms {
                collect_calls_from_expr(&arm.body, out);
            }
        }
        Expr::Constructor(_, inner) => {
            if let Some(inner) = inner {
                collect_calls_from_expr(inner, out);
            }
        }
        Expr::ErrorProp(inner) => collect_calls_from_expr(inner, out),
        Expr::InterpolatedStr(parts) => {
            for p in parts {
                if let crate::ast::StrPart::Parsed(e) = p {
                    collect_calls_from_expr(e, out);
                }
            }
        }
        Expr::List(items) | Expr::Tuple(items) => {
            for item in items {
                collect_calls_from_expr(item, out);
            }
        }
        Expr::MapLiteral(entries) => {
            for (k, v) in entries {
                collect_calls_from_expr(k, out);
                collect_calls_from_expr(v, out);
            }
        }
        Expr::RecordCreate { fields, .. } => {
            for (_, v) in fields {
                collect_calls_from_expr(v, out);
            }
        }
        Expr::RecordUpdate { base, updates, .. } => {
            collect_calls_from_expr(base, out);
            for (_, v) in updates {
                collect_calls_from_expr(v, out);
            }
        }
        Expr::Literal(_) | Expr::Ident(_) | Expr::Resolved(_) => {}
    }
}

fn collect_calls_from_body(body: &FnBody) -> Vec<(String, Vec<&Expr>)> {
    let mut out = Vec::new();
    for stmt in body.stmts() {
        match stmt {
            Stmt::Binding(_, _, expr) | Stmt::Expr(expr) => collect_calls_from_expr(expr, &mut out),
        }
    }
    out
}

fn collect_list_tail_binders_from_expr(
    expr: &Expr,
    list_param_name: &str,
    tails: &mut HashSet<String>,
) {
    match expr {
        Expr::Match { subject, arms, .. } => {
            if matches!(subject.as_ref(), Expr::Ident(id) if id == list_param_name) {
                for MatchArm { pattern, .. } in arms {
                    if let Pattern::Cons(_, tail) = pattern {
                        tails.insert(tail.clone());
                    }
                }
            }
            for arm in arms {
                collect_list_tail_binders_from_expr(&arm.body, list_param_name, tails);
            }
            collect_list_tail_binders_from_expr(subject, list_param_name, tails);
        }
        Expr::FnCall(callee, args) => {
            collect_list_tail_binders_from_expr(callee, list_param_name, tails);
            for arg in args {
                collect_list_tail_binders_from_expr(arg, list_param_name, tails);
            }
        }
        Expr::TailCall(boxed) => {
            let (_, args) = boxed.as_ref();
            for arg in args {
                collect_list_tail_binders_from_expr(arg, list_param_name, tails);
            }
        }
        Expr::Attr(obj, _) => collect_list_tail_binders_from_expr(obj, list_param_name, tails),
        Expr::BinOp(_, left, right) => {
            collect_list_tail_binders_from_expr(left, list_param_name, tails);
            collect_list_tail_binders_from_expr(right, list_param_name, tails);
        }
        Expr::Constructor(_, inner) => {
            if let Some(inner) = inner {
                collect_list_tail_binders_from_expr(inner, list_param_name, tails);
            }
        }
        Expr::ErrorProp(inner) => {
            collect_list_tail_binders_from_expr(inner, list_param_name, tails)
        }
        Expr::InterpolatedStr(parts) => {
            for p in parts {
                if let crate::ast::StrPart::Parsed(e) = p {
                    collect_list_tail_binders_from_expr(e, list_param_name, tails);
                }
            }
        }
        Expr::List(items) | Expr::Tuple(items) => {
            for item in items {
                collect_list_tail_binders_from_expr(item, list_param_name, tails);
            }
        }
        Expr::MapLiteral(entries) => {
            for (k, v) in entries {
                collect_list_tail_binders_from_expr(k, list_param_name, tails);
                collect_list_tail_binders_from_expr(v, list_param_name, tails);
            }
        }
        Expr::RecordCreate { fields, .. } => {
            for (_, v) in fields {
                collect_list_tail_binders_from_expr(v, list_param_name, tails);
            }
        }
        Expr::RecordUpdate { base, updates, .. } => {
            collect_list_tail_binders_from_expr(base, list_param_name, tails);
            for (_, v) in updates {
                collect_list_tail_binders_from_expr(v, list_param_name, tails);
            }
        }
        Expr::Literal(_) | Expr::Ident(_) | Expr::Resolved(_) => {}
    }
}

fn collect_list_tail_binders(fd: &FnDef, list_param_name: &str) -> HashSet<String> {
    let mut tails = HashSet::new();
    for stmt in fd.body.stmts() {
        match stmt {
            Stmt::Binding(_, _, expr) | Stmt::Expr(expr) => {
                collect_list_tail_binders_from_expr(expr, list_param_name, &mut tails)
            }
        }
    }
    tails
}

fn find_type_def<'a>(ctx: &'a CodegenContext, type_name: &str) -> Option<&'a TypeDef> {
    ctx.modules
        .iter()
        .flat_map(|m| m.type_defs.iter())
        .chain(ctx.type_defs.iter())
        .find(|td| toplevel::type_def_name(td) == type_name)
}

fn recursive_constructor_binders(
    td: &TypeDef,
    variant_name: &str,
    binders: &[String],
) -> Vec<String> {
    let variant_short = variant_name.rsplit('.').next().unwrap_or(variant_name);
    match td {
        TypeDef::Sum { name, variants, .. } => variants
            .iter()
            .find(|variant| variant.name == variant_short)
            .map(|variant| {
                variant
                    .fields
                    .iter()
                    .zip(binders.iter())
                    .filter_map(|(field_ty, binder)| {
                        (field_ty.trim() == name).then_some(binder.clone())
                    })
                    .collect()
            })
            .unwrap_or_default(),
        TypeDef::Product { .. } => Vec::new(),
    }
}

fn grow_recursive_subterm_binders_from_expr(
    expr: &Expr,
    tracked: &HashSet<String>,
    td: &TypeDef,
    out: &mut HashSet<String>,
) {
    match expr {
        Expr::Match { subject, arms, .. } => {
            if let Expr::Ident(subject_name) = subject.as_ref()
                && tracked.contains(subject_name)
            {
                for arm in arms {
                    if let Pattern::Constructor(variant_name, binders) = &arm.pattern {
                        out.extend(recursive_constructor_binders(td, variant_name, binders));
                    }
                }
            }
            grow_recursive_subterm_binders_from_expr(subject, tracked, td, out);
            for arm in arms {
                grow_recursive_subterm_binders_from_expr(&arm.body, tracked, td, out);
            }
        }
        Expr::FnCall(callee, args) => {
            grow_recursive_subterm_binders_from_expr(callee, tracked, td, out);
            for arg in args {
                grow_recursive_subterm_binders_from_expr(arg, tracked, td, out);
            }
        }
        Expr::Attr(obj, _) => grow_recursive_subterm_binders_from_expr(obj, tracked, td, out),
        Expr::BinOp(_, left, right) => {
            grow_recursive_subterm_binders_from_expr(left, tracked, td, out);
            grow_recursive_subterm_binders_from_expr(right, tracked, td, out);
        }
        Expr::Constructor(_, Some(inner)) | Expr::ErrorProp(inner) => {
            grow_recursive_subterm_binders_from_expr(inner, tracked, td, out)
        }
        Expr::InterpolatedStr(parts) => {
            for part in parts {
                if let crate::ast::StrPart::Parsed(inner) = part {
                    grow_recursive_subterm_binders_from_expr(inner, tracked, td, out);
                }
            }
        }
        Expr::List(items) | Expr::Tuple(items) => {
            for item in items {
                grow_recursive_subterm_binders_from_expr(item, tracked, td, out);
            }
        }
        Expr::MapLiteral(entries) => {
            for (k, v) in entries {
                grow_recursive_subterm_binders_from_expr(k, tracked, td, out);
                grow_recursive_subterm_binders_from_expr(v, tracked, td, out);
            }
        }
        Expr::RecordCreate { fields, .. } => {
            for (_, v) in fields {
                grow_recursive_subterm_binders_from_expr(v, tracked, td, out);
            }
        }
        Expr::RecordUpdate { base, updates, .. } => {
            grow_recursive_subterm_binders_from_expr(base, tracked, td, out);
            for (_, v) in updates {
                grow_recursive_subterm_binders_from_expr(v, tracked, td, out);
            }
        }
        Expr::TailCall(boxed) => {
            for arg in &boxed.1 {
                grow_recursive_subterm_binders_from_expr(arg, tracked, td, out);
            }
        }
        Expr::Literal(_) | Expr::Ident(_) | Expr::Resolved(_) | Expr::Constructor(_, None) => {}
    }
}

fn collect_recursive_subterm_binders(
    fd: &FnDef,
    param_name: &str,
    param_type: &str,
    ctx: &CodegenContext,
) -> HashSet<String> {
    let Some(td) = find_type_def(ctx, param_type) else {
        return HashSet::new();
    };
    let mut tracked: HashSet<String> = HashSet::from([param_name.to_string()]);
    loop {
        let mut discovered = HashSet::new();
        for stmt in fd.body.stmts() {
            match stmt {
                Stmt::Binding(_, _, expr) | Stmt::Expr(expr) => {
                    grow_recursive_subterm_binders_from_expr(expr, &tracked, td, &mut discovered);
                }
            }
        }
        let before = tracked.len();
        tracked.extend(discovered);
        if tracked.len() == before {
            break;
        }
    }
    tracked.remove(param_name);
    tracked
}

fn single_int_countdown_param_index(fd: &FnDef) -> Option<usize> {
    let recursive_calls: Vec<Vec<&Expr>> = collect_calls_from_body(fd.body.as_ref())
        .into_iter()
        .filter(|(name, _)| call_matches(name, &fd.name))
        .map(|(_, args)| args)
        .collect();
    if recursive_calls.is_empty() {
        return None;
    }

    fd.params
        .iter()
        .enumerate()
        .find_map(|(idx, (param_name, param_ty))| {
            if param_ty != "Int" {
                return None;
            }
            let countdown_ok = recursive_calls.iter().all(|args| {
                args.get(idx)
                    .cloned()
                    .is_some_and(|arg| is_int_minus_positive(arg, param_name))
            });
            if countdown_ok {
                return Some(idx);
            }

            // Negative-guarded ascent (match n < 0) is handled as countdown
            // because the fuel is natAbs(n) which works for both directions.
            let ascent_ok = recursive_calls.iter().all(|args| {
                args.get(idx)
                    .copied()
                    .is_some_and(|arg| is_int_plus_positive(arg, param_name))
            });
            (ascent_ok && has_negative_guarded_ascent(fd, param_name)).then_some(idx)
        })
}

fn has_negative_guarded_ascent(fd: &FnDef, param_name: &str) -> bool {
    let Some(Expr::Match { subject, arms, .. }) = fd.body.tail_expr() else {
        return false;
    };
    let Expr::BinOp(BinOp::Lt, left, right) = subject.as_ref() else {
        return false;
    };
    if !is_ident(left, param_name)
        || !matches!(right.as_ref(), Expr::Literal(crate::ast::Literal::Int(0)))
    {
        return false;
    }

    let mut true_arm = None;
    let mut false_arm = None;
    for arm in arms {
        match arm.pattern {
            Pattern::Literal(crate::ast::Literal::Bool(true)) => true_arm = Some(arm.body.as_ref()),
            Pattern::Literal(crate::ast::Literal::Bool(false)) => {
                false_arm = Some(arm.body.as_ref())
            }
            _ => return false,
        }
    }

    let Some(true_arm) = true_arm else {
        return false;
    };
    let Some(false_arm) = false_arm else {
        return false;
    };

    let mut true_calls = Vec::new();
    collect_calls_from_expr(true_arm, &mut true_calls);
    let mut false_calls = Vec::new();
    collect_calls_from_expr(false_arm, &mut false_calls);

    true_calls
        .iter()
        .any(|(name, _)| call_matches(name, &fd.name))
        && false_calls
            .iter()
            .all(|(name, _)| !call_matches(name, &fd.name))
}

/// Detect ascending-index recursion and extract the bound expression.
/// Returns (param_index, bound_lean_string) if found.
fn single_int_ascending_param(fd: &FnDef) -> Option<(usize, String)> {
    let recursive_calls: Vec<Vec<&Expr>> = collect_calls_from_body(fd.body.as_ref())
        .into_iter()
        .filter(|(name, _)| call_matches(name, &fd.name))
        .map(|(_, args)| args)
        .collect();
    if recursive_calls.is_empty() {
        return None;
    }

    for (idx, (param_name, param_ty)) in fd.params.iter().enumerate() {
        if param_ty != "Int" {
            continue;
        }
        let ascent_ok = recursive_calls.iter().all(|args| {
            args.get(idx)
                .cloned()
                .is_some_and(|arg| is_int_plus_positive(arg, param_name))
        });
        if !ascent_ok {
            continue;
        }
        if let Some(bound_lean) = extract_equality_bound_lean(fd, param_name) {
            return Some((idx, bound_lean));
        }
    }
    None
}

/// Extract the bound expression from `match param == BOUND` as a Lean string.
fn extract_equality_bound_lean(fd: &FnDef, param_name: &str) -> Option<String> {
    let Expr::Match { subject, arms, .. } = fd.body.tail_expr()? else {
        return None;
    };
    let Expr::BinOp(BinOp::Eq, left, right) = subject.as_ref() else {
        return None;
    };
    if !is_ident(left, param_name) {
        return None;
    }
    // Verify: true arm = base (no self-call), false arm = recursive (has self-call)
    let mut true_has_self = false;
    let mut false_has_self = false;
    for arm in arms {
        match arm.pattern {
            Pattern::Literal(crate::ast::Literal::Bool(true)) => {
                let mut calls = Vec::new();
                collect_calls_from_expr(&arm.body, &mut calls);
                true_has_self = calls.iter().any(|(n, _)| call_matches(n, &fd.name));
            }
            Pattern::Literal(crate::ast::Literal::Bool(false)) => {
                let mut calls = Vec::new();
                collect_calls_from_expr(&arm.body, &mut calls);
                false_has_self = calls.iter().any(|(n, _)| call_matches(n, &fd.name));
            }
            _ => return None,
        }
    }
    if true_has_self || !false_has_self {
        return None;
    }
    // Convert bound expr to Lean string — works for literals and simple expressions
    Some(bound_expr_to_lean(right))
}

fn bound_expr_to_lean(expr: &Expr) -> String {
    match expr {
        Expr::Literal(crate::ast::Literal::Int(n)) => format!("{}", n),
        Expr::Ident(name) => expr::aver_name_to_lean(name),
        Expr::FnCall(f, args) => {
            if let Some(dotted) = crate::codegen::common::expr_to_dotted_name(f) {
                // List.len(xs) → xs.length in Lean
                if dotted == "List.len" && args.len() == 1 {
                    return format!("{}.length", bound_expr_to_lean(&args[0]));
                }
                let lean_args: Vec<String> = args.iter().map(bound_expr_to_lean).collect();
                format!(
                    "({} {})",
                    expr::aver_name_to_lean(&dotted),
                    lean_args.join(" ")
                )
            } else {
                "0".to_string()
            }
        }
        Expr::Attr(obj, field) => format!(
            "{}.{}",
            bound_expr_to_lean(obj),
            expr::aver_name_to_lean(field)
        ),
        _ => "0".to_string(),
    }
}

fn supports_single_sizeof_structural(fd: &FnDef, ctx: &CodegenContext) -> bool {
    let recursive_calls: Vec<Vec<&Expr>> = collect_calls_from_body(fd.body.as_ref())
        .into_iter()
        .filter(|(name, _)| call_matches(name, &fd.name))
        .map(|(_, args)| args)
        .collect();
    if recursive_calls.is_empty() {
        return false;
    }

    let metric_indices = sizeof_measure_param_indices(fd);
    if metric_indices.is_empty() {
        return false;
    }

    let binder_sets: HashMap<usize, HashSet<String>> = metric_indices
        .iter()
        .filter_map(|idx| {
            let (param_name, param_type) = fd.params.get(*idx)?;
            recursive_type_names(ctx).contains(param_type).then(|| {
                (
                    *idx,
                    collect_recursive_subterm_binders(fd, param_name, param_type, ctx),
                )
            })
        })
        .collect();

    if binder_sets.values().all(HashSet::is_empty) {
        return false;
    }

    recursive_calls.iter().all(|args| {
        let mut strictly_smaller = false;
        for idx in &metric_indices {
            let Some((param_name, _)) = fd.params.get(*idx) else {
                return false;
            };
            let Some(arg) = args.get(*idx).cloned() else {
                return false;
            };
            if is_ident(arg, param_name) {
                continue;
            }
            let Some(binders) = binder_sets.get(idx) else {
                return false;
            };
            if matches!(arg, Expr::Ident(id) if binders.contains(id)) {
                strictly_smaller = true;
                continue;
            }
            return false;
        }
        strictly_smaller
    })
}

fn single_list_structural_param_index(fd: &FnDef) -> Option<usize> {
    fd.params
        .iter()
        .enumerate()
        .find_map(|(param_index, (param_name, param_ty))| {
            if !(param_ty.starts_with("List<") || param_ty == "List") {
                return None;
            }

            let tails = collect_list_tail_binders(fd, param_name);
            if tails.is_empty() {
                return None;
            }

            let recursive_calls: Vec<Option<&Expr>> = collect_calls_from_body(fd.body.as_ref())
                .into_iter()
                .filter(|(name, _)| call_matches(name, &fd.name))
                .map(|(_, args)| args.get(param_index).cloned())
                .collect();
            if recursive_calls.is_empty() {
                return None;
            }

            recursive_calls
                .into_iter()
                .all(|arg| {
                    matches!(
                        arg,
                        Some(Expr::Ident(id)) if tails.contains(id)
                    )
                })
                .then_some(param_index)
        })
}

fn is_ident(expr: &Expr, name: &str) -> bool {
    matches!(expr, Expr::Ident(id) if id == name)
}

fn is_int_plus_positive(expr: &Expr, param_name: &str) -> bool {
    match expr {
        Expr::BinOp(BinOp::Add, left, right) => {
            matches!(left.as_ref(), Expr::Ident(id) if id == param_name)
                && matches!(right.as_ref(), Expr::Literal(crate::ast::Literal::Int(n)) if *n >= 1)
        }
        Expr::FnCall(callee, args) => {
            let Some(name) = expr_to_dotted_name(callee) else {
                return false;
            };
            (name == "Int.add" || name == "int.add")
                && args.len() == 2
                && matches!(&args[0], Expr::Ident(id) if id == param_name)
                && matches!(&args[1], Expr::Literal(crate::ast::Literal::Int(n)) if *n >= 1)
        }
        _ => false,
    }
}

fn is_skip_ws_advance(expr: &Expr, string_param: &str, pos_param: &str) -> bool {
    let Expr::FnCall(callee, args) = expr else {
        return false;
    };
    let Some(name) = expr_to_dotted_name(callee) else {
        return false;
    };
    if !call_matches(&name, "skipWs") || args.len() != 2 {
        return false;
    }
    is_ident(&args[0], string_param) && is_int_plus_positive(&args[1], pos_param)
}

fn is_skip_ws_same(expr: &Expr, string_param: &str, pos_param: &str) -> bool {
    let Expr::FnCall(callee, args) = expr else {
        return false;
    };
    let Some(name) = expr_to_dotted_name(callee) else {
        return false;
    };
    if !call_matches(&name, "skipWs") || args.len() != 2 {
        return false;
    }
    is_ident(&args[0], string_param) && is_ident(&args[1], pos_param)
}

fn is_string_pos_advance(expr: &Expr, string_param: &str, pos_param: &str) -> bool {
    is_int_plus_positive(expr, pos_param) || is_skip_ws_advance(expr, string_param, pos_param)
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum StringPosEdge {
    Same,
    Advance,
}

fn classify_string_pos_edge(
    expr: &Expr,
    string_param: &str,
    pos_param: &str,
) -> Option<StringPosEdge> {
    if is_ident(expr, pos_param) || is_skip_ws_same(expr, string_param, pos_param) {
        return Some(StringPosEdge::Same);
    }
    if is_string_pos_advance(expr, string_param, pos_param) {
        return Some(StringPosEdge::Advance);
    }
    if let Expr::FnCall(callee, args) = expr {
        let name = expr_to_dotted_name(callee)?;
        if call_matches(&name, "skipWs")
            && args.len() == 2
            && is_ident(&args[0], string_param)
            && matches!(&args[1], Expr::Ident(id) if id != pos_param)
        {
            return Some(StringPosEdge::Advance);
        }
    }
    if matches!(expr, Expr::Ident(id) if id != pos_param) {
        return Some(StringPosEdge::Advance);
    }
    None
}

fn ranks_from_same_edges(
    names: &HashSet<String>,
    same_edges: &HashMap<String, HashSet<String>>,
) -> Option<HashMap<String, usize>> {
    let mut indegree: HashMap<String, usize> = names.iter().map(|n| (n.clone(), 0)).collect();
    for outs in same_edges.values() {
        for to in outs {
            if let Some(entry) = indegree.get_mut(to) {
                *entry += 1;
            } else {
                return None;
            }
        }
    }

    let mut queue: Vec<String> = indegree
        .iter()
        .filter_map(|(name, &deg)| (deg == 0).then_some(name.clone()))
        .collect();
    queue.sort();
    let mut topo = Vec::new();
    while let Some(node) = queue.pop() {
        topo.push(node.clone());
        let outs = same_edges.get(&node).cloned().unwrap_or_default();
        let mut newly_zero = Vec::new();
        for to in outs {
            if let Some(entry) = indegree.get_mut(&to) {
                *entry -= 1;
                if *entry == 0 {
                    newly_zero.push(to);
                }
            } else {
                return None;
            }
        }
        newly_zero.sort();
        queue.extend(newly_zero);
    }

    if topo.len() != names.len() {
        return None;
    }

    let n = topo.len();
    let mut ranks = HashMap::new();
    for (idx, name) in topo.into_iter().enumerate() {
        ranks.insert(name, n - idx);
    }
    Some(ranks)
}

fn supports_single_string_pos_advance(fd: &FnDef) -> bool {
    let Some((string_param, string_ty)) = fd.params.first() else {
        return false;
    };
    let Some((pos_param, pos_ty)) = fd.params.get(1) else {
        return false;
    };
    if string_ty != "String" || pos_ty != "Int" {
        return false;
    }

    let recursive_calls: Vec<(Option<&Expr>, Option<&Expr>)> =
        collect_calls_from_body(fd.body.as_ref())
            .into_iter()
            .filter(|(name, _)| call_matches(name, &fd.name))
            .map(|(_, args)| (args.first().cloned(), args.get(1).cloned()))
            .collect();
    if recursive_calls.is_empty() {
        return false;
    }

    recursive_calls.into_iter().all(|(arg0, arg1)| {
        arg0.is_some_and(|e| is_ident(e, string_param))
            && arg1.is_some_and(|e| is_string_pos_advance(e, string_param, pos_param))
    })
}

fn supports_mutual_int_countdown(component: &[&FnDef]) -> bool {
    if component.len() < 2 {
        return false;
    }
    if component
        .iter()
        .any(|fd| !matches!(fd.params.first(), Some((_, t)) if t == "Int"))
    {
        return false;
    }
    let names: HashSet<String> = component.iter().map(|fd| fd.name.clone()).collect();
    let mut any_intra = false;
    for fd in component {
        let param_name = &fd.params[0].0;
        for (callee, args) in collect_calls_from_body(fd.body.as_ref()) {
            if !call_is_in_set(&callee, &names) {
                continue;
            }
            any_intra = true;
            let Some(arg0) = args.first().cloned() else {
                return false;
            };
            if !is_int_minus_positive(arg0, param_name) {
                return false;
            }
        }
    }
    any_intra
}

fn supports_mutual_string_pos_advance(component: &[&FnDef]) -> Option<HashMap<String, usize>> {
    if component.len() < 2 {
        return None;
    }
    if component.iter().any(|fd| {
        !matches!(fd.params.first(), Some((_, t)) if t == "String")
            || !matches!(fd.params.get(1), Some((_, t)) if t == "Int")
    }) {
        return None;
    }

    let names: HashSet<String> = component.iter().map(|fd| fd.name.clone()).collect();
    let mut same_edges: HashMap<String, HashSet<String>> =
        names.iter().map(|n| (n.clone(), HashSet::new())).collect();
    let mut any_intra = false;

    for fd in component {
        let string_param = &fd.params[0].0;
        let pos_param = &fd.params[1].0;
        for (callee_raw, args) in collect_calls_from_body(fd.body.as_ref()) {
            let Some(callee) = canonical_callee_name(&callee_raw, &names) else {
                continue;
            };
            any_intra = true;

            let arg0 = args.first().cloned()?;
            let arg1 = args.get(1).cloned()?;

            if !is_ident(arg0, string_param) {
                return None;
            }

            match classify_string_pos_edge(arg1, string_param, pos_param) {
                Some(StringPosEdge::Same) => {
                    if let Some(edges) = same_edges.get_mut(&fd.name) {
                        edges.insert(callee);
                    } else {
                        return None;
                    }
                }
                Some(StringPosEdge::Advance) => {}
                None => return None,
            }
        }
    }

    if !any_intra {
        return None;
    }

    ranks_from_same_edges(&names, &same_edges)
}

fn is_scalar_like_type(type_name: &str) -> bool {
    matches!(
        type_name,
        "Int" | "Float" | "Bool" | "String" | "Char" | "Byte" | "Unit"
    )
}

pub(super) fn sizeof_measure_param_indices(fd: &FnDef) -> Vec<usize> {
    fd.params
        .iter()
        .enumerate()
        .filter_map(|(idx, (_, type_name))| (!is_scalar_like_type(type_name)).then_some(idx))
        .collect()
}

fn supports_mutual_sizeof_ranked(component: &[&FnDef]) -> Option<HashMap<String, usize>> {
    if component.len() < 2 {
        return None;
    }
    let names: HashSet<String> = component.iter().map(|fd| fd.name.clone()).collect();
    let metric_indices: HashMap<String, Vec<usize>> = component
        .iter()
        .map(|fd| (fd.name.clone(), sizeof_measure_param_indices(fd)))
        .collect();
    if component.iter().any(|fd| {
        metric_indices
            .get(&fd.name)
            .is_none_or(|indices| indices.is_empty())
    }) {
        return None;
    }

    let mut same_edges: HashMap<String, HashSet<String>> =
        names.iter().map(|n| (n.clone(), HashSet::new())).collect();
    let mut any_intra = false;
    for fd in component {
        let caller_metric_indices = metric_indices.get(&fd.name)?;
        let caller_metric_params: Vec<&str> = caller_metric_indices
            .iter()
            .filter_map(|idx| fd.params.get(*idx).map(|(name, _)| name.as_str()))
            .collect();
        for (callee_raw, args) in collect_calls_from_body(fd.body.as_ref()) {
            let Some(callee) = canonical_callee_name(&callee_raw, &names) else {
                continue;
            };
            any_intra = true;
            let callee_metric_indices = metric_indices.get(&callee)?;
            let is_same_edge = callee_metric_indices.len() == caller_metric_params.len()
                && callee_metric_indices
                    .iter()
                    .enumerate()
                    .all(|(pos, callee_idx)| {
                        let Some(arg) = args.get(*callee_idx).cloned() else {
                            return false;
                        };
                        is_ident(arg, caller_metric_params[pos])
                    });
            if is_same_edge {
                if let Some(edges) = same_edges.get_mut(&fd.name) {
                    edges.insert(callee);
                } else {
                    return None;
                }
            }
        }
    }
    if !any_intra {
        return None;
    }

    let ranks = ranks_from_same_edges(&names, &same_edges)?;
    let mut out = HashMap::new();
    for fd in component {
        let rank = ranks.get(&fd.name).cloned()?;
        out.insert(fd.name.clone(), rank);
    }
    Some(out)
}

fn proof_mode_recursion_analysis(
    ctx: &CodegenContext,
) -> (HashMap<String, RecursionPlan>, Vec<ProofModeIssue>) {
    let mut plans = HashMap::new();
    let mut issues = Vec::new();

    let all_pure = pure_fns(ctx);
    let recursive_names = recursive_pure_fn_names(ctx);
    let components = call_graph::ordered_fn_components(&all_pure, &ctx.module_prefixes);

    for component in components {
        if component.is_empty() {
            continue;
        }
        let is_recursive_component =
            component.len() > 1 || recursive_names.contains(&component[0].name);
        if !is_recursive_component {
            continue;
        }

        if component.len() > 1 {
            if supports_mutual_int_countdown(&component) {
                for fd in &component {
                    plans.insert(fd.name.clone(), RecursionPlan::MutualIntCountdown);
                }
            } else if let Some(ranks) = supports_mutual_string_pos_advance(&component) {
                for fd in &component {
                    if let Some(rank) = ranks.get(&fd.name).cloned() {
                        plans.insert(
                            fd.name.clone(),
                            RecursionPlan::MutualStringPosAdvance { rank },
                        );
                    }
                }
            } else if let Some(rankings) = supports_mutual_sizeof_ranked(&component) {
                for fd in &component {
                    if let Some(rank) = rankings.get(&fd.name).cloned() {
                        plans.insert(fd.name.clone(), RecursionPlan::MutualSizeOfRanked { rank });
                    }
                }
            } else {
                let names = component
                    .iter()
                    .map(|fd| fd.name.clone())
                    .collect::<Vec<_>>()
                    .join(", ");
                let line = component.iter().map(|fd| fd.line).min().unwrap_or(1);
                issues.push(ProofModeIssue {
                    line,
                    message: format!(
                        "unsupported mutual recursion group (currently supported in proof mode: Int countdown on first param): {}",
                        names
                    ),
                });
            }
            continue;
        }

        let fd = component[0];
        if recurrence::detect_second_order_int_linear_recurrence(fd).is_some() {
            plans.insert(fd.name.clone(), RecursionPlan::LinearRecurrence2);
        } else if let Some((param_index, bound_lean)) = single_int_ascending_param(fd) {
            plans.insert(
                fd.name.clone(),
                RecursionPlan::IntAscending {
                    param_index,
                    bound_lean,
                },
            );
        } else if let Some(param_index) = single_int_countdown_param_index(fd) {
            plans.insert(fd.name.clone(), RecursionPlan::IntCountdown { param_index });
        } else if supports_single_sizeof_structural(fd, ctx) {
            plans.insert(fd.name.clone(), RecursionPlan::SizeOfStructural);
        } else if let Some(param_index) = single_list_structural_param_index(fd) {
            plans.insert(
                fd.name.clone(),
                RecursionPlan::ListStructural { param_index },
            );
        } else if supports_single_string_pos_advance(fd) {
            plans.insert(fd.name.clone(), RecursionPlan::StringPosAdvance);
        } else {
            issues.push(ProofModeIssue {
                line: fd.line,
                message: format!(
                    "recursive function '{}' is outside proof subset (currently supported: Int countdown, second-order affine Int recurrences with pair-state worker, structural recursion on List/recursive ADTs, String+position, mutual Int countdown, mutual String+position, and ranked sizeOf recursion)",
                    fd.name
                ),
            });
        }
    }

    (plans, issues)
}

/// Proof-mode diagnostics for Lean transpilation.
///
/// Returns human-readable notices for recursive shapes that still fall back to
/// regular `partial` Lean defs instead of total proof-mode emission.
pub fn proof_mode_findings(ctx: &CodegenContext) -> Vec<ProofModeIssue> {
    let (_plans, issues) = proof_mode_recursion_analysis(ctx);
    issues
}

pub fn proof_mode_issues(ctx: &CodegenContext) -> Vec<String> {
    proof_mode_findings(ctx)
        .into_iter()
        .map(|issue| issue.message)
        .collect()
}

/// Transpile an Aver program to a Lean 4 project.
pub fn transpile(ctx: &CodegenContext) -> ProjectOutput {
    transpile_with_verify_mode(ctx, VerifyEmitMode::NativeDecide)
}

/// Proof-mode transpilation.
///
/// Uses recursion plans validated by `proof_mode_issues` and emits supported
/// recursive functions without `partial`, adding `termination_by` scaffolding.
pub fn transpile_for_proof_mode(
    ctx: &CodegenContext,
    verify_mode: VerifyEmitMode,
) -> ProjectOutput {
    let (plans, _issues) = proof_mode_recursion_analysis(ctx);
    let recursive_names = recursive_pure_fn_names(ctx);
    let recursive_types = recursive_type_names(ctx);

    let mut sections = Vec::new();

    // Reuse the same type emission as standard mode.
    for module in &ctx.modules {
        for td in &module.type_defs {
            sections.push(toplevel::emit_type_def(td));
            if toplevel::is_recursive_type_def(td) {
                sections.push(toplevel::emit_recursive_decidable_eq(
                    toplevel::type_def_name(td),
                ));
                if let Some(measure) = toplevel::emit_recursive_measure(td, &recursive_types) {
                    sections.push(measure);
                }
            }
            sections.push(String::new());
        }
    }
    for td in &ctx.type_defs {
        sections.push(toplevel::emit_type_def(td));
        if toplevel::is_recursive_type_def(td) {
            sections.push(toplevel::emit_recursive_decidable_eq(
                toplevel::type_def_name(td),
            ));
            if let Some(measure) = toplevel::emit_recursive_measure(td, &recursive_types) {
                sections.push(measure);
            }
        }
        sections.push(String::new());
    }

    emit_pure_functions_proof(ctx, &plans, &recursive_names, &mut sections);

    for item in &ctx.items {
        if let TopLevel::Decision(db) = item {
            sections.push(toplevel::emit_decision(db));
            sections.push(String::new());
        }
    }

    let mut verify_case_counters: HashMap<String, usize> = HashMap::new();
    for item in &ctx.items {
        if let TopLevel::Verify(vb) = item {
            let key = verify_counter_key(vb);
            let start_idx = *verify_case_counters.get(&key).unwrap_or(&0);
            let (emitted, next_idx) = toplevel::emit_verify_block(vb, ctx, verify_mode, start_idx);
            verify_case_counters.insert(key, next_idx);
            sections.push(emitted);
            sections.push(String::new());
        }
    }

    let lean_body = sections.join("\n");
    let prelude = generate_prelude_for_body(&lean_body, false);
    let lean_source = format!("{prelude}\n\n{lean_body}");
    let project_name = lean_project_name(ctx);
    let lakefile = generate_lakefile(&project_name);
    let toolchain = generate_toolchain();
    ProjectOutput {
        files: vec![
            ("lakefile.lean".to_string(), lakefile),
            ("lean-toolchain".to_string(), toolchain),
            (format!("{}.lean", project_name), lean_source),
        ],
    }
}

/// Transpile an Aver program to a Lean 4 project with configurable verify proof mode.
///
/// - `NativeDecide` emits `example ... := by native_decide`
/// - `Sorry` emits `example ... := by sorry`
/// - `TheoremSkeleton` emits named theorem skeletons with `sorry`
pub fn transpile_with_verify_mode(
    ctx: &CodegenContext,
    verify_mode: VerifyEmitMode,
) -> ProjectOutput {
    let mut sections = Vec::new();

    // Detect recursive functions for `partial` annotation
    let recursive_fns = call_graph::find_recursive_fns(&ctx.items);

    // Module type definitions (from depends)
    for module in &ctx.modules {
        for td in &module.type_defs {
            sections.push(toplevel::emit_type_def(td));
            // #18: Recursive types need unsafe DecidableEq instance
            if toplevel::is_recursive_type_def(td) {
                sections.push(toplevel::emit_recursive_decidable_eq(
                    toplevel::type_def_name(td),
                ));
            }
            sections.push(String::new());
        }
    }

    // Type definitions
    for td in &ctx.type_defs {
        sections.push(toplevel::emit_type_def(td));
        // #18: Recursive types need unsafe DecidableEq instance
        if toplevel::is_recursive_type_def(td) {
            sections.push(toplevel::emit_recursive_decidable_eq(
                toplevel::type_def_name(td),
            ));
        }
        sections.push(String::new());
    }

    // Emit pure functions in SCC-topological order:
    // callees first, then callers; SCCs as `mutual` blocks.
    emit_pure_functions(ctx, &recursive_fns, &mut sections);

    // Decision blocks (as comments)
    for item in &ctx.items {
        if let TopLevel::Decision(db) = item {
            sections.push(toplevel::emit_decision(db));
            sections.push(String::new());
        }
    }

    // Verify blocks → proof items (`native_decide` by default, optional `sorry`/theorem stubs).
    let mut verify_case_counters: HashMap<String, usize> = HashMap::new();
    for item in &ctx.items {
        if let TopLevel::Verify(vb) = item {
            let key = verify_counter_key(vb);
            let start_idx = *verify_case_counters.get(&key).unwrap_or(&0);
            let (emitted, next_idx) = toplevel::emit_verify_block(vb, ctx, verify_mode, start_idx);
            verify_case_counters.insert(key, next_idx);
            sections.push(emitted);
            sections.push(String::new());
        }
    }

    let lean_body = sections.join("\n");
    let prelude = generate_prelude_for_body(&lean_body, false);
    let lean_source = format!("{prelude}\n\n{lean_body}");

    // Project files
    let project_name = lean_project_name(ctx);
    let lakefile = generate_lakefile(&project_name);
    let toolchain = generate_toolchain();

    ProjectOutput {
        files: vec![
            ("lakefile.lean".to_string(), lakefile),
            ("lean-toolchain".to_string(), toolchain),
            (format!("{}.lean", project_name), lean_source),
        ],
    }
}

fn emit_pure_functions(
    ctx: &CodegenContext,
    recursive_fns: &HashSet<String>,
    sections: &mut Vec<String>,
) {
    let all_fns: Vec<&FnDef> = ctx
        .modules
        .iter()
        .flat_map(|m| m.fn_defs.iter())
        .chain(ctx.fn_defs.iter())
        .filter(|fd| toplevel::is_pure_fn(fd))
        .collect();
    if all_fns.is_empty() {
        return;
    }

    let components = call_graph::ordered_fn_components(&all_fns, &ctx.module_prefixes);
    for fns in components {
        if fns.is_empty() {
            continue;
        }

        // Multi-node SCC => emit `mutual ... end`.
        if fns.len() > 1 {
            sections.push(toplevel::emit_mutual_group(&fns, ctx));
            sections.push(String::new());
            continue;
        }

        // Singleton SCC => regular `def` (recursive singletons still get `partial`
        // via `recursive_fns` in emit_fn_def).
        if let Some(code) = toplevel::emit_fn_def(fns[0], recursive_fns, ctx) {
            sections.push(code);
            sections.push(String::new());
        }
    }
}

fn emit_pure_functions_proof(
    ctx: &CodegenContext,
    plans: &HashMap<String, RecursionPlan>,
    recursive_names: &HashSet<String>,
    sections: &mut Vec<String>,
) {
    let all_fns: Vec<&FnDef> = pure_fns(ctx);
    if all_fns.is_empty() {
        return;
    }

    let components = call_graph::ordered_fn_components(&all_fns, &ctx.module_prefixes);
    for fns in components {
        if fns.is_empty() {
            continue;
        }
        if fns.len() > 1 {
            let all_supported = fns.iter().all(|fd| plans.contains_key(&fd.name));
            if all_supported {
                sections.push(toplevel::emit_mutual_group_proof(&fns, ctx, plans));
            } else {
                sections.push(toplevel::emit_mutual_group(&fns, ctx));
            }
            sections.push(String::new());
            continue;
        }

        let fd = fns[0];
        let is_recursive = recursive_names.contains(&fd.name);
        let emitted = if is_recursive && !plans.contains_key(&fd.name) {
            toplevel::emit_fn_def(fd, recursive_names, ctx)
        } else {
            toplevel::emit_fn_def_proof(fd, plans.get(&fd.name).cloned(), ctx)
        };
        if let Some(code) = emitted {
            sections.push(code);
            sections.push(String::new());
        }
    }
}

#[cfg(test)]
fn generate_prelude() -> String {
    generate_prelude_for_body("", true)
}

fn generate_prelude_for_body(body: &str, include_all_helpers: bool) -> String {
    let mut parts = vec![
        LEAN_PRELUDE_HEADER.to_string(),
        LEAN_PRELUDE_FLOAT_COE.to_string(),
        LEAN_PRELUDE_FLOAT_DEC_EQ.to_string(),
        LEAN_PRELUDE_EXCEPT_DEC_EQ.to_string(),
        LEAN_PRELUDE_EXCEPT_NS.to_string(),
        LEAN_PRELUDE_OPTION_TO_EXCEPT.to_string(),
        LEAN_PRELUDE_STRING_HADD.to_string(),
    ];

    if include_all_helpers || needs_builtin_named_type(body, "Header") {
        parts.push(LEAN_PRELUDE_HEADER_TYPE.to_string());
    }
    if include_all_helpers || needs_builtin_named_type(body, "HttpResponse") {
        parts.push(LEAN_PRELUDE_HTTP_RESPONSE_TYPE.to_string());
    }
    if include_all_helpers || needs_builtin_named_type(body, "HttpRequest") {
        parts.push(LEAN_PRELUDE_HTTP_REQUEST_TYPE.to_string());
    }
    if include_all_helpers || needs_builtin_named_type(body, "Tcp_Connection") {
        parts.push(LEAN_PRELUDE_TCP_CONNECTION_TYPE.to_string());
    }

    if include_all_helpers || body.contains("averStringPosFuel") {
        parts.push(LEAN_PRELUDE_PROOF_FUEL.to_string());
    }

    if include_all_helpers || body.contains("AverMeasure.") {
        parts.push(LEAN_PRELUDE_AVER_MEASURE.to_string());
    }

    if include_all_helpers || body.contains("AverMap.") {
        parts.push(generate_map_prelude(body, include_all_helpers));
    }

    parts.extend([
        LEAN_PRELUDE_AVER_LIST.to_string(),
        LEAN_PRELUDE_STRING_HELPERS.to_string(),
        LEAN_PRELUDE_NUMERIC_PARSE.to_string(),
        LEAN_PRELUDE_CHAR_BYTE.to_string(),
    ]);

    parts.join("\n\n")
}

fn needs_builtin_named_type(body: &str, type_name: &str) -> bool {
    references_named_type(body, type_name) && !declares_named_type(body, type_name)
}

fn references_named_type(body: &str, type_name: &str) -> bool {
    let mut token = String::new();
    for ch in body.chars() {
        if ch.is_ascii_alphanumeric() || ch == '_' || ch == '.' {
            token.push(ch);
            continue;
        }
        if token == type_name {
            return true;
        }
        token.clear();
    }
    token == type_name
}

fn declares_named_type(body: &str, type_name: &str) -> bool {
    let structure_decl = format!("structure {} where", type_name);
    let inductive_decl = format!("inductive {} where", type_name);
    body.lines()
        .map(str::trim_start)
        .any(|line| line == structure_decl || line == inductive_decl)
}

fn generate_map_prelude(body: &str, include_all_helpers: bool) -> String {
    let mut parts = vec![AVER_MAP_PRELUDE_BASE.to_string()];

    let needs_has_set_self = include_all_helpers || body.contains("AverMap.has_set_self");
    let needs_get_set_self = include_all_helpers || body.contains("AverMap.get_set_self");
    let needs_get_set_other = include_all_helpers
        || body.contains("AverMap.get_set_other")
        || body.contains("AverMap.has_set_other");
    let needs_has_set_other = include_all_helpers || body.contains("AverMap.has_set_other");

    if needs_has_set_self {
        parts.push(AVER_MAP_PRELUDE_HAS_SET_SELF.to_string());
    }
    if needs_get_set_self {
        parts.push(AVER_MAP_PRELUDE_GET_SET_SELF.to_string());
    }
    if needs_get_set_other {
        parts.push(AVER_MAP_PRELUDE_GET_SET_OTHER.to_string());
    }
    if needs_has_set_other {
        parts.push(AVER_MAP_PRELUDE_HAS_SET_OTHER.to_string());
    }

    parts.push(AVER_MAP_PRELUDE_END.to_string());
    parts.join("\n\n")
}

fn generate_lakefile(project_name: &str) -> String {
    format!(
        r#"import Lake
open Lake DSL

package «{}» where
  version := v!"0.1.0"

@[default_target]
lean_lib «{}» where
  srcDir := "."
"#,
        project_name.to_lowercase(),
        project_name
    )
}

fn generate_toolchain() -> String {
    "leanprover/lean4:v4.15.0\n".to_string()
}

fn capitalize_first(s: &str) -> String {
    let mut chars = s.chars();
    match chars.next() {
        None => String::new(),
        Some(c) => c.to_uppercase().to_string() + chars.as_str(),
    }
}

#[cfg(test)]
mod tests {
    use super::{
        VerifyEmitMode, generate_prelude, proof_mode_issues, recurrence, transpile,
        transpile_for_proof_mode, transpile_with_verify_mode,
    };
    use crate::ast::{
        BinOp, Expr, FnBody, FnDef, Literal, MatchArm, Pattern, Stmt, TopLevel, TypeDef,
        TypeVariant, VerifyBlock, VerifyGiven, VerifyGivenDomain, VerifyKind, VerifyLaw,
    };
    use crate::codegen::{CodegenContext, build_context};
    use crate::source::parse_source;
    use crate::tco;
    use crate::types::checker::run_type_check_full;
    use std::collections::{HashMap, HashSet};
    use std::rc::Rc;

    fn empty_ctx() -> CodegenContext {
        CodegenContext {
            items: vec![],
            fn_sigs: HashMap::new(),
            memo_fns: HashSet::new(),
            memo_safe_types: HashSet::new(),
            type_defs: vec![],
            fn_defs: vec![],
            project_name: "verify_mode".to_string(),
            modules: vec![],
            module_prefixes: HashSet::new(),
            policy: None,
            emit_replay_runtime: false,
            runtime_policy_from_env: false,
            guest_entry: None,
            emit_self_host_support: false,
            extra_fn_defs: Vec::new(),
            mutual_tco_members: HashSet::new(),
        }
    }

    fn ctx_from_source(source: &str, project_name: &str) -> CodegenContext {
        let mut items = parse_source(source).expect("source should parse");
        tco::transform_program(&mut items);
        let tc = run_type_check_full(&items, None);
        assert!(
            tc.errors.is_empty(),
            "source should typecheck without errors: {:?}",
            tc.errors
        );
        build_context(items, &tc, HashSet::new(), project_name.to_string(), vec![])
    }

    fn generated_lean_file(out: &crate::codegen::ProjectOutput) -> &str {
        out.files
            .iter()
            .find_map(|(name, content)| {
                (name.ends_with(".lean") && name != "lakefile.lean").then_some(content.as_str())
            })
            .expect("expected generated Lean file")
    }

    fn empty_ctx_with_verify_case() -> CodegenContext {
        let mut ctx = empty_ctx();
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "f".to_string(),
            line: 1,
            cases: vec![(
                Expr::Literal(Literal::Int(1)),
                Expr::Literal(Literal::Int(1)),
            )],
            kind: VerifyKind::Cases,
        }));
        ctx
    }

    fn empty_ctx_with_two_verify_blocks_same_fn() -> CodegenContext {
        let mut ctx = empty_ctx();
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "f".to_string(),
            line: 1,
            cases: vec![(
                Expr::Literal(Literal::Int(1)),
                Expr::Literal(Literal::Int(1)),
            )],
            kind: VerifyKind::Cases,
        }));
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "f".to_string(),
            line: 2,
            cases: vec![(
                Expr::Literal(Literal::Int(2)),
                Expr::Literal(Literal::Int(2)),
            )],
            kind: VerifyKind::Cases,
        }));
        ctx
    }

    fn empty_ctx_with_verify_law() -> CodegenContext {
        let mut ctx = empty_ctx();
        let add = FnDef {
            name: "add".to_string(),
            line: 1,
            params: vec![
                ("a".to_string(), "Int".to_string()),
                ("b".to_string(), "Int".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::BinOp(
                BinOp::Add,
                Box::new(Expr::Ident("a".to_string())),
                Box::new(Expr::Ident("b".to_string())),
            ))),
            resolution: None,
        };
        ctx.fn_defs.push(add.clone());
        ctx.items.push(TopLevel::FnDef(add));
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "add".to_string(),
            line: 1,
            cases: vec![
                (
                    Expr::FnCall(
                        Box::new(Expr::Ident("add".to_string())),
                        vec![
                            Expr::Literal(Literal::Int(1)),
                            Expr::Literal(Literal::Int(2)),
                        ],
                    ),
                    Expr::FnCall(
                        Box::new(Expr::Ident("add".to_string())),
                        vec![
                            Expr::Literal(Literal::Int(2)),
                            Expr::Literal(Literal::Int(1)),
                        ],
                    ),
                ),
                (
                    Expr::FnCall(
                        Box::new(Expr::Ident("add".to_string())),
                        vec![
                            Expr::Literal(Literal::Int(2)),
                            Expr::Literal(Literal::Int(3)),
                        ],
                    ),
                    Expr::FnCall(
                        Box::new(Expr::Ident("add".to_string())),
                        vec![
                            Expr::Literal(Literal::Int(3)),
                            Expr::Literal(Literal::Int(2)),
                        ],
                    ),
                ),
            ],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "commutative".to_string(),
                givens: vec![
                    VerifyGiven {
                        name: "a".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::IntRange { start: 1, end: 2 },
                    },
                    VerifyGiven {
                        name: "b".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![
                            Expr::Literal(Literal::Int(2)),
                            Expr::Literal(Literal::Int(3)),
                        ]),
                    },
                ],
                when: None,
                lhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![Expr::Ident("a".to_string()), Expr::Ident("b".to_string())],
                ),
                rhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![Expr::Ident("b".to_string()), Expr::Ident("a".to_string())],
                ),
                sample_guards: vec![],
            })),
        }));
        ctx
    }

    #[test]
    fn prelude_normalizes_float_string_format() {
        let prelude = generate_prelude();
        assert!(
            prelude.contains("private def normalizeFloatString (s : String) : String :="),
            "missing normalizeFloatString helper in prelude"
        );
        assert!(
            prelude.contains(
                "def String.fromFloat (f : Float) : String := normalizeFloatString (toString f)"
            ),
            "String.fromFloat should normalize Lean float formatting"
        );
    }

    #[test]
    fn prelude_validates_char_from_code_unicode_bounds() {
        let prelude = generate_prelude();
        assert!(
            prelude.contains("if n < 0 || n > 1114111 then none"),
            "Char.fromCode should reject code points above Unicode max"
        );
        assert!(
            prelude.contains("else if n >= 55296 && n <= 57343 then none"),
            "Char.fromCode should reject surrogate code points"
        );
    }

    #[test]
    fn prelude_includes_map_set_helper_lemmas() {
        let prelude = generate_prelude();
        assert!(
            prelude.contains("theorem has_set_self [DecidableEq α]"),
            "missing AverMap.has_set_self helper theorem"
        );
        assert!(
            prelude.contains("theorem get_set_self [DecidableEq α]"),
            "missing AverMap.get_set_self helper theorem"
        );
    }

    #[test]
    fn lean_output_without_map_usage_omits_map_prelude() {
        let ctx = ctx_from_source(
            r#"
module NoMap
    intent = "Simple pure program without maps."

fn addOne(n: Int) -> Int
    n + 1

verify addOne
    addOne(1) => 2
"#,
            "nomap",
        );
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        assert!(
            !lean.contains("namespace AverMap"),
            "did not expect AverMap prelude in program without map usage:\n{}",
            lean
        );
    }

    #[test]
    fn transpile_emits_native_decide_for_verify_by_default() {
        let out = transpile(&empty_ctx_with_verify_case());
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("example : 1 = 1 := by native_decide"));
    }

    #[test]
    fn transpile_can_emit_sorry_for_verify_when_requested() {
        let out = transpile_with_verify_mode(&empty_ctx_with_verify_case(), VerifyEmitMode::Sorry);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("example : 1 = 1 := by sorry"));
    }

    #[test]
    fn transpile_can_emit_theorem_skeletons_for_verify() {
        let out = transpile_with_verify_mode(
            &empty_ctx_with_verify_case(),
            VerifyEmitMode::TheoremSkeleton,
        );
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("theorem f_verify_1 : 1 = 1 := by"));
        assert!(lean.contains("  sorry"));
    }

    #[test]
    fn theorem_skeleton_numbering_is_global_per_function_across_verify_blocks() {
        let out = transpile_with_verify_mode(
            &empty_ctx_with_two_verify_blocks_same_fn(),
            VerifyEmitMode::TheoremSkeleton,
        );
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("theorem f_verify_1 : 1 = 1 := by"));
        assert!(lean.contains("theorem f_verify_2 : 2 = 2 := by"));
    }

    #[test]
    fn transpile_emits_named_theorems_for_verify_law() {
        let out = transpile(&empty_ctx_with_verify_law());
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("-- verify law add.commutative (2 cases)"));
        assert!(lean.contains("-- given a: Int = 1..2"));
        assert!(lean.contains("-- given b: Int = [2, 3]"));
        assert!(lean.contains(
            "theorem add_law_commutative : ∀ (a : Int) (b : Int), add a b = add b a := by"
        ));
        assert!(lean.contains("  intro a b"));
        assert!(lean.contains("  simp [add, Int.add_comm]"));
        assert!(lean.contains(
            "theorem add_law_commutative_sample_1 : add 1 2 = add 2 1 := by native_decide"
        ));
        assert!(lean.contains(
            "theorem add_law_commutative_sample_2 : add 2 3 = add 3 2 := by native_decide"
        ));
    }

    #[test]
    fn generate_prelude_emits_int_roundtrip_theorem() {
        let lean = generate_prelude();
        assert!(lean.contains(
            "theorem Int.fromString_fromInt : ∀ n : Int, Int.fromString (String.fromInt n) = .ok n"
        ));
        assert!(lean.contains("theorem String.intercalate_empty_chars (s : String) :"));
        assert!(lean.contains("def splitOnCharGo"));
        assert!(lean.contains("theorem split_single_char_append"));
        assert!(lean.contains("theorem split_intercalate_trailing_single_char"));
        assert!(lean.contains("namespace AverDigits"));
        assert!(lean.contains("theorem String.charAt_length_none (s : String)"));
        assert!(lean.contains("theorem digitChar_not_ws : ∀ d : Nat, d < 10 ->"));
    }

    #[test]
    fn transpile_emits_guarded_theorems_for_verify_law_when_clause() {
        let ctx = ctx_from_source(
            r#"
module GuardedLaw
    intent =
        "verify law with precondition"

fn pickGreater(a: Int, b: Int) -> Int
    match a > b
        true -> a
        false -> b

verify pickGreater law ordered
    given a: Int = [1, 2]
    given b: Int = [1, 2]
    when a > b
    pickGreater(a, b) => a
"#,
            "guarded_law",
        );
        let out = transpile_with_verify_mode(&ctx, VerifyEmitMode::TheoremSkeleton);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("-- when (a > b)"));
        assert!(lean.contains(
            "theorem pickGreater_law_ordered : ∀ (a : Int) (b : Int), a = 1 ∨ a = 2 -> b = 1 ∨ b = 2 -> (a > b) = true -> pickGreater a b = a := by"
        ));
        assert!(lean.contains(
            "theorem pickGreater_law_ordered_sample_1 : (1 > 1) = true -> pickGreater 1 1 = 1 := by"
        ));
        assert!(lean.contains(
            "theorem pickGreater_law_ordered_sample_4 : (2 > 2) = true -> pickGreater 2 2 = 2 := by"
        ));
    }

    #[test]
    fn transpile_uses_spec_theorem_names_for_declared_spec_laws() {
        let ctx = ctx_from_source(
            r#"
module SpecDemo
    intent =
        "spec demo"

fn absVal(x: Int) -> Int
    match x < 0
        true -> 0 - x
        false -> x

fn absValSpec(x: Int) -> Int
    match x < 0
        true -> 0 - x
        false -> x

verify absVal law absValSpec
    given x: Int = [-2, -1, 0, 1, 2]
    absVal(x) => absValSpec(x)
"#,
            "spec_demo",
        );
        let out = transpile_with_verify_mode(&ctx, VerifyEmitMode::TheoremSkeleton);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("-- verify law absVal.spec absValSpec (5 cases)"));
        assert!(
            lean.contains(
                "theorem absVal_eq_absValSpec : ∀ (x : Int), absVal x = absValSpec x := by"
            )
        );
        assert!(lean.contains("theorem absVal_eq_absValSpec_checked_domain :"));
        assert!(lean.contains("theorem absVal_eq_absValSpec_sample_1 :"));
        assert!(!lean.contains("theorem absVal_law_absValSpec :"));
    }

    #[test]
    fn transpile_keeps_noncanonical_spec_laws_as_regular_law_names() {
        let ctx = ctx_from_source(
            r#"
module SpecLawShape
    intent =
        "shape probe"

fn foo(x: Int) -> Int
    x + 1

fn fooSpec(seed: Int, x: Int) -> Int
    x + seed

verify foo law fooSpec
    given x: Int = [1, 2]
    foo(x) => fooSpec(1, x)
"#,
            "spec_law_shape",
        );
        let out = transpile_with_verify_mode(&ctx, VerifyEmitMode::TheoremSkeleton);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("-- verify law foo.fooSpec (2 cases)"));
        assert!(lean.contains("theorem foo_law_fooSpec : ∀ (x : Int), foo x = fooSpec 1 x := by"));
        assert!(!lean.contains("theorem foo_eq_fooSpec :"));
    }

    #[test]
    fn transpile_auto_proves_linear_int_canonical_spec_law_in_auto_mode() {
        let ctx = ctx_from_source(
            r#"
module SpecGap
    intent =
        "nontrivial canonical spec law"

fn inc(x: Int) -> Int
    x + 1

fn incSpec(x: Int) -> Int
    x + 2 - 1

verify inc law incSpec
    given x: Int = [0, 1, 2]
    inc(x) => incSpec(x)
"#,
            "spec_gap",
        );
        let out = transpile(&ctx);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("-- verify law inc.spec incSpec (3 cases)"));
        assert!(lean.contains("theorem inc_eq_incSpec : ∀ (x : Int), inc x = incSpec x := by"));
        assert!(lean.contains("change (x + 1) = ((x + 2) - 1)"));
        assert!(lean.contains("omega"));
        assert!(!lean.contains(
            "-- universal theorem inc_eq_incSpec omitted: sampled law shape is not auto-proved yet"
        ));
        assert!(lean.contains("theorem inc_eq_incSpec_checked_domain :"));
    }

    #[test]
    fn transpile_auto_proves_guarded_canonical_spec_law_in_auto_mode() {
        let ctx = ctx_from_source(
            r#"
module GuardedSpecGap
    intent =
        "guarded canonical spec law"

fn clampNonNegative(x: Int) -> Int
    match x < 0
        true -> 0
        false -> x

fn clampNonNegativeSpec(x: Int) -> Int
    match x < 0
        true -> 0
        false -> x

verify clampNonNegative law clampNonNegativeSpec
    given x: Int = [-2, -1, 0, 1, 2]
    when x >= 0
    clampNonNegative(x) => clampNonNegativeSpec(x)
"#,
            "guarded_spec_gap",
        );
        let out = transpile(&ctx);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("-- when (x >= 0)"));
        assert!(lean.contains(
            "theorem clampNonNegative_eq_clampNonNegativeSpec : ∀ (x : Int), x = (-2) ∨ x = (-1) ∨ x = 0 ∨ x = 1 ∨ x = 2 -> (x >= 0) = true -> clampNonNegative x = clampNonNegativeSpec x := by"
        ));
        assert!(lean.contains("intro x h_x h_when"));
        assert!(lean.contains("simpa [clampNonNegative, clampNonNegativeSpec]"));
        assert!(!lean.contains(
            "-- universal theorem clampNonNegative_eq_clampNonNegativeSpec omitted: sampled law shape is not auto-proved yet"
        ));
        assert!(!lean.contains("cases h_x"));
    }

    #[test]
    fn transpile_auto_proves_simp_normalized_canonical_spec_law_in_auto_mode() {
        let ctx = ctx_from_source(
            r#"
module SpecGapNonlinear
    intent =
        "nonlinear canonical spec law"

fn square(x: Int) -> Int
    x * x

fn squareSpec(x: Int) -> Int
    x * x + 0

verify square law squareSpec
    given x: Int = [0, 1, 2]
    square(x) => squareSpec(x)
"#,
            "spec_gap_nonlinear",
        );
        let out = transpile(&ctx);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("-- verify law square.spec squareSpec (3 cases)"));
        assert!(
            lean.contains(
                "theorem square_eq_squareSpec : ∀ (x : Int), square x = squareSpec x := by"
            )
        );
        assert!(lean.contains("simp [square, squareSpec]"));
        assert!(!lean.contains(
            "-- universal theorem square_eq_squareSpec omitted: sampled law shape is not auto-proved yet"
        ));
        assert!(lean.contains("theorem square_eq_squareSpec_checked_domain :"));
        assert!(lean.contains("theorem square_eq_squareSpec_sample_1 :"));
    }

    #[test]
    fn transpile_auto_proves_reflexive_law_with_rfl() {
        let mut ctx = empty_ctx();
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "idLaw".to_string(),
            line: 1,
            cases: vec![(
                Expr::Literal(Literal::Int(1)),
                Expr::Literal(Literal::Int(1)),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "reflexive".to_string(),
                givens: vec![VerifyGiven {
                    name: "x".to_string(),
                    type_name: "Int".to_string(),
                    domain: VerifyGivenDomain::IntRange { start: 1, end: 2 },
                }],
                when: None,
                lhs: Expr::Ident("x".to_string()),
                rhs: Expr::Ident("x".to_string()),
                sample_guards: vec![],
            })),
        }));
        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("theorem idLaw_law_reflexive : ∀ (x : Int), x = x := by"));
        assert!(lean.contains("  intro x"));
        assert!(lean.contains("  rfl"));
    }

    #[test]
    fn transpile_auto_proves_identity_law_for_int_add_wrapper() {
        let mut ctx = empty_ctx_with_verify_law();
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "add".to_string(),
            line: 10,
            cases: vec![(
                Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::Literal(Literal::Int(1)),
                        Expr::Literal(Literal::Int(0)),
                    ],
                ),
                Expr::Literal(Literal::Int(1)),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "identityZero".to_string(),
                givens: vec![VerifyGiven {
                    name: "a".to_string(),
                    type_name: "Int".to_string(),
                    domain: VerifyGivenDomain::Explicit(vec![
                        Expr::Literal(Literal::Int(0)),
                        Expr::Literal(Literal::Int(1)),
                    ]),
                }],
                when: None,
                lhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![Expr::Ident("a".to_string()), Expr::Literal(Literal::Int(0))],
                ),
                rhs: Expr::Ident("a".to_string()),
                sample_guards: vec![],
            })),
        }));
        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("theorem add_law_identityZero : ∀ (a : Int), add a 0 = a := by"));
        assert!(lean.contains("  intro a"));
        assert!(lean.contains("  simp [add]"));
    }

    #[test]
    fn transpile_auto_proves_associative_law_for_int_add_wrapper() {
        let mut ctx = empty_ctx_with_verify_law();
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "add".to_string(),
            line: 20,
            cases: vec![(
                Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::FnCall(
                            Box::new(Expr::Ident("add".to_string())),
                            vec![
                                Expr::Literal(Literal::Int(1)),
                                Expr::Literal(Literal::Int(2)),
                            ],
                        ),
                        Expr::Literal(Literal::Int(3)),
                    ],
                ),
                Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::Literal(Literal::Int(1)),
                        Expr::FnCall(
                            Box::new(Expr::Ident("add".to_string())),
                            vec![
                                Expr::Literal(Literal::Int(2)),
                                Expr::Literal(Literal::Int(3)),
                            ],
                        ),
                    ],
                ),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "associative".to_string(),
                givens: vec![
                    VerifyGiven {
                        name: "a".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(1))]),
                    },
                    VerifyGiven {
                        name: "b".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(2))]),
                    },
                    VerifyGiven {
                        name: "c".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(3))]),
                    },
                ],
                when: None,
                lhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::FnCall(
                            Box::new(Expr::Ident("add".to_string())),
                            vec![Expr::Ident("a".to_string()), Expr::Ident("b".to_string())],
                        ),
                        Expr::Ident("c".to_string()),
                    ],
                ),
                rhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::Ident("a".to_string()),
                        Expr::FnCall(
                            Box::new(Expr::Ident("add".to_string())),
                            vec![Expr::Ident("b".to_string()), Expr::Ident("c".to_string())],
                        ),
                    ],
                ),
                sample_guards: vec![],
            })),
        }));
        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains(
            "theorem add_law_associative : ∀ (a : Int) (b : Int) (c : Int), add (add a b) c = add a (add b c) := by"
        ));
        assert!(lean.contains("  intro a b c"));
        assert!(lean.contains("  simp [add, Int.add_assoc]"));
    }

    #[test]
    fn transpile_auto_proves_sub_laws() {
        let mut ctx = empty_ctx();
        let sub = FnDef {
            name: "sub".to_string(),
            line: 1,
            params: vec![
                ("a".to_string(), "Int".to_string()),
                ("b".to_string(), "Int".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::BinOp(
                BinOp::Sub,
                Box::new(Expr::Ident("a".to_string())),
                Box::new(Expr::Ident("b".to_string())),
            ))),
            resolution: None,
        };
        ctx.fn_defs.push(sub.clone());
        ctx.items.push(TopLevel::FnDef(sub));

        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "sub".to_string(),
            line: 10,
            cases: vec![(
                Expr::FnCall(
                    Box::new(Expr::Ident("sub".to_string())),
                    vec![
                        Expr::Literal(Literal::Int(2)),
                        Expr::Literal(Literal::Int(0)),
                    ],
                ),
                Expr::Literal(Literal::Int(2)),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "rightIdentity".to_string(),
                givens: vec![VerifyGiven {
                    name: "a".to_string(),
                    type_name: "Int".to_string(),
                    domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(2))]),
                }],
                when: None,
                lhs: Expr::FnCall(
                    Box::new(Expr::Ident("sub".to_string())),
                    vec![Expr::Ident("a".to_string()), Expr::Literal(Literal::Int(0))],
                ),
                rhs: Expr::Ident("a".to_string()),
                sample_guards: vec![],
            })),
        }));
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "sub".to_string(),
            line: 20,
            cases: vec![(
                Expr::FnCall(
                    Box::new(Expr::Ident("sub".to_string())),
                    vec![
                        Expr::Literal(Literal::Int(2)),
                        Expr::Literal(Literal::Int(1)),
                    ],
                ),
                Expr::BinOp(
                    BinOp::Sub,
                    Box::new(Expr::Literal(Literal::Int(0))),
                    Box::new(Expr::FnCall(
                        Box::new(Expr::Ident("sub".to_string())),
                        vec![
                            Expr::Literal(Literal::Int(1)),
                            Expr::Literal(Literal::Int(2)),
                        ],
                    )),
                ),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "antiCommutative".to_string(),
                givens: vec![
                    VerifyGiven {
                        name: "a".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(2))]),
                    },
                    VerifyGiven {
                        name: "b".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(1))]),
                    },
                ],
                when: None,
                lhs: Expr::FnCall(
                    Box::new(Expr::Ident("sub".to_string())),
                    vec![Expr::Ident("a".to_string()), Expr::Ident("b".to_string())],
                ),
                rhs: Expr::BinOp(
                    BinOp::Sub,
                    Box::new(Expr::Literal(Literal::Int(0))),
                    Box::new(Expr::FnCall(
                        Box::new(Expr::Ident("sub".to_string())),
                        vec![Expr::Ident("b".to_string()), Expr::Ident("a".to_string())],
                    )),
                ),
                sample_guards: vec![],
            })),
        }));

        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("theorem sub_law_rightIdentity : ∀ (a : Int), sub a 0 = a := by"));
        assert!(lean.contains("  simp [sub]"));
        assert!(lean.contains(
            "theorem sub_law_antiCommutative : ∀ (a : Int) (b : Int), sub a b = (-sub b a) := by"
        ));
        assert!(lean.contains("  simpa [sub] using (Int.neg_sub b a).symm"));
    }

    #[test]
    fn transpile_auto_proves_unary_wrapper_equivalence_law() {
        let mut ctx = empty_ctx();
        let add = FnDef {
            name: "add".to_string(),
            line: 1,
            params: vec![
                ("a".to_string(), "Int".to_string()),
                ("b".to_string(), "Int".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::BinOp(
                BinOp::Add,
                Box::new(Expr::Ident("a".to_string())),
                Box::new(Expr::Ident("b".to_string())),
            ))),
            resolution: None,
        };
        let add_one = FnDef {
            name: "addOne".to_string(),
            line: 2,
            params: vec![("n".to_string(), "Int".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::BinOp(
                BinOp::Add,
                Box::new(Expr::Ident("n".to_string())),
                Box::new(Expr::Literal(Literal::Int(1))),
            ))),
            resolution: None,
        };
        ctx.fn_defs.push(add.clone());
        ctx.fn_defs.push(add_one.clone());
        ctx.items.push(TopLevel::FnDef(add));
        ctx.items.push(TopLevel::FnDef(add_one));
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "addOne".to_string(),
            line: 3,
            cases: vec![(
                Expr::FnCall(
                    Box::new(Expr::Ident("addOne".to_string())),
                    vec![Expr::Literal(Literal::Int(2))],
                ),
                Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::Literal(Literal::Int(2)),
                        Expr::Literal(Literal::Int(1)),
                    ],
                ),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "identityViaAdd".to_string(),
                givens: vec![VerifyGiven {
                    name: "n".to_string(),
                    type_name: "Int".to_string(),
                    domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(2))]),
                }],
                when: None,
                lhs: Expr::FnCall(
                    Box::new(Expr::Ident("addOne".to_string())),
                    vec![Expr::Ident("n".to_string())],
                ),
                rhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![Expr::Ident("n".to_string()), Expr::Literal(Literal::Int(1))],
                ),
                sample_guards: vec![],
            })),
        }));
        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(
            lean.contains(
                "theorem addOne_law_identityViaAdd : ∀ (n : Int), addOne n = add n 1 := by"
            )
        );
        assert!(lean.contains("  simp [addOne, add]"));
    }

    #[test]
    fn transpile_auto_proves_direct_map_set_laws() {
        let mut ctx = empty_ctx();

        let map_set = |m: Expr, k: Expr, v: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Map".to_string())),
                    "set".to_string(),
                )),
                vec![m, k, v],
            )
        };
        let map_has = |m: Expr, k: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Map".to_string())),
                    "has".to_string(),
                )),
                vec![m, k],
            )
        };
        let map_get = |m: Expr, k: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Map".to_string())),
                    "get".to_string(),
                )),
                vec![m, k],
            )
        };
        let some = |v: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Option".to_string())),
                    "Some".to_string(),
                )),
                vec![v],
            )
        };

        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "map".to_string(),
            line: 1,
            cases: vec![(
                map_has(
                    map_set(
                        Expr::Ident("m".to_string()),
                        Expr::Ident("k".to_string()),
                        Expr::Ident("v".to_string()),
                    ),
                    Expr::Ident("k".to_string()),
                ),
                Expr::Literal(Literal::Bool(true)),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "setHasKey".to_string(),
                givens: vec![
                    VerifyGiven {
                        name: "m".to_string(),
                        type_name: "Map<String, Int>".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::FnCall(
                            Box::new(Expr::Attr(
                                Box::new(Expr::Ident("Map".to_string())),
                                "empty".to_string(),
                            )),
                            vec![],
                        )]),
                    },
                    VerifyGiven {
                        name: "k".to_string(),
                        type_name: "String".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Str(
                            "a".to_string(),
                        ))]),
                    },
                    VerifyGiven {
                        name: "v".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(1))]),
                    },
                ],
                when: None,
                lhs: map_has(
                    map_set(
                        Expr::Ident("m".to_string()),
                        Expr::Ident("k".to_string()),
                        Expr::Ident("v".to_string()),
                    ),
                    Expr::Ident("k".to_string()),
                ),
                rhs: Expr::Literal(Literal::Bool(true)),
                sample_guards: vec![],
            })),
        }));

        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "map".to_string(),
            line: 2,
            cases: vec![(
                map_get(
                    map_set(
                        Expr::Ident("m".to_string()),
                        Expr::Ident("k".to_string()),
                        Expr::Ident("v".to_string()),
                    ),
                    Expr::Ident("k".to_string()),
                ),
                some(Expr::Ident("v".to_string())),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "setGetKey".to_string(),
                givens: vec![
                    VerifyGiven {
                        name: "m".to_string(),
                        type_name: "Map<String, Int>".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::FnCall(
                            Box::new(Expr::Attr(
                                Box::new(Expr::Ident("Map".to_string())),
                                "empty".to_string(),
                            )),
                            vec![],
                        )]),
                    },
                    VerifyGiven {
                        name: "k".to_string(),
                        type_name: "String".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Str(
                            "a".to_string(),
                        ))]),
                    },
                    VerifyGiven {
                        name: "v".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(1))]),
                    },
                ],
                when: None,
                lhs: map_get(
                    map_set(
                        Expr::Ident("m".to_string()),
                        Expr::Ident("k".to_string()),
                        Expr::Ident("v".to_string()),
                    ),
                    Expr::Ident("k".to_string()),
                ),
                rhs: some(Expr::Ident("v".to_string())),
                sample_guards: vec![],
            })),
        }));

        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("simpa using AverMap.has_set_self m k v"));
        assert!(lean.contains("simpa using AverMap.get_set_self m k v"));
    }

    #[test]
    fn transpile_auto_proves_direct_recursive_sum_law_by_structural_induction() {
        let ctx = ctx_from_source(
            r#"
module Mirror
    intent =
        "direct recursive sum induction probe"

type Tree
    Leaf(Int)
    Node(Tree, Tree)

fn mirror(t: Tree) -> Tree
    match t
        Tree.Leaf(v) -> Tree.Leaf(v)
        Tree.Node(left, right) -> Tree.Node(mirror(right), mirror(left))

verify mirror law involutive
    given t: Tree = [Tree.Leaf(1), Tree.Node(Tree.Leaf(1), Tree.Leaf(2))]
    mirror(mirror(t)) => t
"#,
            "mirror",
        );
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        assert!(
            lean.contains(
                "theorem mirror_law_involutive : ∀ (t : Tree), mirror (mirror t) = t := by"
            )
        );
        assert!(lean.contains("  induction t with"));
        assert!(lean.contains("  | leaf f0 => simp [mirror]"));
        assert!(lean.contains("  | node f0 f1 ih0 ih1 => simp_all [mirror]"));
        assert!(!lean.contains(
            "-- universal theorem mirror_law_involutive omitted: sampled law shape is not auto-proved yet"
        ));
    }

    #[test]
    fn transpile_auto_proves_map_update_laws() {
        let mut ctx = empty_ctx();

        let map_get = |m: Expr, k: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Map".to_string())),
                    "get".to_string(),
                )),
                vec![m, k],
            )
        };
        let map_set = |m: Expr, k: Expr, v: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Map".to_string())),
                    "set".to_string(),
                )),
                vec![m, k, v],
            )
        };
        let map_has = |m: Expr, k: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Map".to_string())),
                    "has".to_string(),
                )),
                vec![m, k],
            )
        };
        let option_some = |v: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Option".to_string())),
                    "Some".to_string(),
                )),
                vec![v],
            )
        };
        let option_with_default = |opt: Expr, def: Expr| {
            Expr::FnCall(
                Box::new(Expr::Attr(
                    Box::new(Expr::Ident("Option".to_string())),
                    "withDefault".to_string(),
                )),
                vec![opt, def],
            )
        };

        let add_one = FnDef {
            name: "addOne".to_string(),
            line: 1,
            params: vec![("n".to_string(), "Int".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::BinOp(
                BinOp::Add,
                Box::new(Expr::Ident("n".to_string())),
                Box::new(Expr::Literal(Literal::Int(1))),
            ))),
            resolution: None,
        };
        ctx.fn_defs.push(add_one.clone());
        ctx.items.push(TopLevel::FnDef(add_one));

        let inc_count = FnDef {
            name: "incCount".to_string(),
            line: 2,
            params: vec![
                ("counts".to_string(), "Map<String, Int>".to_string()),
                ("word".to_string(), "String".to_string()),
            ],
            return_type: "Map<String, Int>".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::Block(vec![
                Stmt::Binding(
                    "current".to_string(),
                    None,
                    map_get(
                        Expr::Ident("counts".to_string()),
                        Expr::Ident("word".to_string()),
                    ),
                ),
                Stmt::Expr(Expr::Match {
                    subject: Box::new(Expr::Ident("current".to_string())),
                    arms: vec![
                        MatchArm {
                            pattern: Pattern::Constructor(
                                "Option.Some".to_string(),
                                vec!["n".to_string()],
                            ),
                            body: Box::new(map_set(
                                Expr::Ident("counts".to_string()),
                                Expr::Ident("word".to_string()),
                                Expr::BinOp(
                                    BinOp::Add,
                                    Box::new(Expr::Ident("n".to_string())),
                                    Box::new(Expr::Literal(Literal::Int(1))),
                                ),
                            )),
                        },
                        MatchArm {
                            pattern: Pattern::Constructor("Option.None".to_string(), vec![]),
                            body: Box::new(map_set(
                                Expr::Ident("counts".to_string()),
                                Expr::Ident("word".to_string()),
                                Expr::Literal(Literal::Int(1)),
                            )),
                        },
                    ],
                    line: 2,
                }),
            ])),
            resolution: None,
        };
        ctx.fn_defs.push(inc_count.clone());
        ctx.items.push(TopLevel::FnDef(inc_count));

        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "incCount".to_string(),
            line: 10,
            cases: vec![(
                map_has(
                    Expr::FnCall(
                        Box::new(Expr::Ident("incCount".to_string())),
                        vec![
                            Expr::Ident("counts".to_string()),
                            Expr::Ident("word".to_string()),
                        ],
                    ),
                    Expr::Ident("word".to_string()),
                ),
                Expr::Literal(Literal::Bool(true)),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "keyPresent".to_string(),
                givens: vec![
                    VerifyGiven {
                        name: "counts".to_string(),
                        type_name: "Map<String, Int>".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::FnCall(
                            Box::new(Expr::Attr(
                                Box::new(Expr::Ident("Map".to_string())),
                                "empty".to_string(),
                            )),
                            vec![],
                        )]),
                    },
                    VerifyGiven {
                        name: "word".to_string(),
                        type_name: "String".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Str(
                            "a".to_string(),
                        ))]),
                    },
                ],
                when: None,
                lhs: map_has(
                    Expr::FnCall(
                        Box::new(Expr::Ident("incCount".to_string())),
                        vec![
                            Expr::Ident("counts".to_string()),
                            Expr::Ident("word".to_string()),
                        ],
                    ),
                    Expr::Ident("word".to_string()),
                ),
                rhs: Expr::Literal(Literal::Bool(true)),
                sample_guards: vec![],
            })),
        }));

        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "incCount".to_string(),
            line: 20,
            cases: vec![(
                map_get(
                    Expr::FnCall(
                        Box::new(Expr::Ident("incCount".to_string())),
                        vec![
                            Expr::Ident("counts".to_string()),
                            Expr::Literal(Literal::Str("a".to_string())),
                        ],
                    ),
                    Expr::Literal(Literal::Str("a".to_string())),
                ),
                option_some(Expr::FnCall(
                    Box::new(Expr::Ident("addOne".to_string())),
                    vec![option_with_default(
                        map_get(
                            Expr::Ident("counts".to_string()),
                            Expr::Literal(Literal::Str("a".to_string())),
                        ),
                        Expr::Literal(Literal::Int(0)),
                    )],
                )),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "existingKeyIncrements".to_string(),
                givens: vec![VerifyGiven {
                    name: "counts".to_string(),
                    type_name: "Map<String, Int>".to_string(),
                    domain: VerifyGivenDomain::Explicit(vec![Expr::FnCall(
                        Box::new(Expr::Attr(
                            Box::new(Expr::Ident("Map".to_string())),
                            "empty".to_string(),
                        )),
                        vec![],
                    )]),
                }],
                when: None,
                lhs: map_get(
                    Expr::FnCall(
                        Box::new(Expr::Ident("incCount".to_string())),
                        vec![
                            Expr::Ident("counts".to_string()),
                            Expr::Literal(Literal::Str("a".to_string())),
                        ],
                    ),
                    Expr::Literal(Literal::Str("a".to_string())),
                ),
                rhs: option_some(Expr::FnCall(
                    Box::new(Expr::Ident("addOne".to_string())),
                    vec![option_with_default(
                        map_get(
                            Expr::Ident("counts".to_string()),
                            Expr::Literal(Literal::Str("a".to_string())),
                        ),
                        Expr::Literal(Literal::Int(0)),
                    )],
                )),
                sample_guards: vec![],
            })),
        }));

        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(
            lean.contains("cases h : AverMap.get counts word <;> simp [AverMap.has_set_self]"),
            "expected keyPresent auto-proof with has_set_self"
        );
        assert!(
            lean.contains("cases h : AverMap.get counts \"a\" <;> simp [AverMap.get_set_self, addOne, incCount]"),
            "expected existingKeyIncrements auto-proof with get_set_self"
        );
    }

    #[test]
    fn transpile_parenthesizes_negative_int_call_args_in_law_samples() {
        let mut ctx = empty_ctx();
        let add = FnDef {
            name: "add".to_string(),
            line: 1,
            params: vec![
                ("a".to_string(), "Int".to_string()),
                ("b".to_string(), "Int".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::BinOp(
                BinOp::Add,
                Box::new(Expr::Ident("a".to_string())),
                Box::new(Expr::Ident("b".to_string())),
            ))),
            resolution: None,
        };
        ctx.fn_defs.push(add.clone());
        ctx.items.push(TopLevel::FnDef(add));
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "add".to_string(),
            line: 1,
            cases: vec![(
                Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::Literal(Literal::Int(-2)),
                        Expr::Literal(Literal::Int(-1)),
                    ],
                ),
                Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![
                        Expr::Literal(Literal::Int(-1)),
                        Expr::Literal(Literal::Int(-2)),
                    ],
                ),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "commutative".to_string(),
                givens: vec![
                    VerifyGiven {
                        name: "a".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(-2))]),
                    },
                    VerifyGiven {
                        name: "b".to_string(),
                        type_name: "Int".to_string(),
                        domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(-1))]),
                    },
                ],
                when: None,
                lhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![Expr::Ident("a".to_string()), Expr::Ident("b".to_string())],
                ),
                rhs: Expr::FnCall(
                    Box::new(Expr::Ident("add".to_string())),
                    vec![Expr::Ident("b".to_string()), Expr::Ident("a".to_string())],
                ),
                sample_guards: vec![],
            })),
        }));

        let out = transpile(&ctx);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains(
            "theorem add_law_commutative_sample_1 : add (-2) (-1) = add (-1) (-2) := by native_decide"
        ));
    }

    #[test]
    fn verify_law_numbering_is_scoped_per_law_name() {
        let mut ctx = empty_ctx();
        let f = FnDef {
            name: "f".to_string(),
            line: 1,
            params: vec![("x".to_string(), "Int".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Ident("x".to_string()))),
            resolution: None,
        };
        ctx.fn_defs.push(f.clone());
        ctx.items.push(TopLevel::FnDef(f));
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "f".to_string(),
            line: 1,
            cases: vec![(
                Expr::Literal(Literal::Int(1)),
                Expr::Literal(Literal::Int(1)),
            )],
            kind: VerifyKind::Cases,
        }));
        ctx.items.push(TopLevel::Verify(VerifyBlock {
            fn_name: "f".to_string(),
            line: 2,
            cases: vec![(
                Expr::Literal(Literal::Int(2)),
                Expr::Literal(Literal::Int(2)),
            )],
            kind: VerifyKind::Law(Box::new(VerifyLaw {
                name: "identity".to_string(),
                givens: vec![VerifyGiven {
                    name: "x".to_string(),
                    type_name: "Int".to_string(),
                    domain: VerifyGivenDomain::Explicit(vec![Expr::Literal(Literal::Int(2))]),
                }],
                when: None,
                lhs: Expr::Ident("x".to_string()),
                rhs: Expr::Ident("x".to_string()),
                sample_guards: vec![],
            })),
        }));
        let out = transpile_with_verify_mode(&ctx, VerifyEmitMode::TheoremSkeleton);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("theorem f_verify_1 : 1 = 1 := by"));
        assert!(lean.contains("theorem f_law_identity : ∀ (x : Int), x = x := by"));
        assert!(lean.contains("theorem f_law_identity_sample_1 : 2 = 2 := by"));
        assert!(!lean.contains("theorem f_law_identity_sample_2 : 2 = 2 := by"));
    }

    #[test]
    fn proof_mode_accepts_single_int_countdown_recursion() {
        let mut ctx = empty_ctx();
        let down = FnDef {
            name: "down".to_string(),
            line: 1,
            params: vec![("n".to_string(), "Int".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::Ident("n".to_string())),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Int(0)),
                        body: Box::new(Expr::Literal(Literal::Int(0))),
                    },
                    MatchArm {
                        pattern: Pattern::Wildcard,
                        body: Box::new(Expr::TailCall(Box::new((
                            "down".to_string(),
                            vec![Expr::BinOp(
                                BinOp::Sub,
                                Box::new(Expr::Ident("n".to_string())),
                                Box::new(Expr::Literal(Literal::Int(1))),
                            )],
                        )))),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(down.clone()));
        ctx.fn_defs.push(down);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected Int countdown recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("def down__fuel"));
        assert!(lean.contains("def down (n : Int) : Int :="));
        assert!(lean.contains("down__fuel ((Int.natAbs n) + 1) n"));
    }

    #[test]
    fn proof_mode_accepts_single_int_countdown_on_nonfirst_param() {
        let mut ctx = empty_ctx();
        let repeat_like = FnDef {
            name: "repeatLike".to_string(),
            line: 1,
            params: vec![
                ("char".to_string(), "String".to_string()),
                ("n".to_string(), "Int".to_string()),
            ],
            return_type: "List<String>".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::BinOp(
                    BinOp::Lte,
                    Box::new(Expr::Ident("n".to_string())),
                    Box::new(Expr::Literal(Literal::Int(0))),
                )),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Bool(true)),
                        body: Box::new(Expr::List(vec![])),
                    },
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Bool(false)),
                        body: Box::new(Expr::TailCall(Box::new((
                            "repeatLike".to_string(),
                            vec![
                                Expr::Ident("char".to_string()),
                                Expr::BinOp(
                                    BinOp::Sub,
                                    Box::new(Expr::Ident("n".to_string())),
                                    Box::new(Expr::Literal(Literal::Int(1))),
                                ),
                            ],
                        )))),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(repeat_like.clone()));
        ctx.fn_defs.push(repeat_like);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected non-first Int countdown recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("def repeatLike__fuel"));
        assert!(lean.contains("def repeatLike (char : String) (n : Int) : List String :="));
        assert!(lean.contains("repeatLike__fuel ((Int.natAbs n) + 1) char n"));
    }

    #[test]
    fn proof_mode_accepts_negative_guarded_int_ascent() {
        let mut ctx = empty_ctx();
        let normalize = FnDef {
            name: "normalize".to_string(),
            line: 1,
            params: vec![("angle".to_string(), "Int".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::BinOp(
                    BinOp::Lt,
                    Box::new(Expr::Ident("angle".to_string())),
                    Box::new(Expr::Literal(Literal::Int(0))),
                )),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Bool(true)),
                        body: Box::new(Expr::TailCall(Box::new((
                            "normalize".to_string(),
                            vec![Expr::BinOp(
                                BinOp::Add,
                                Box::new(Expr::Ident("angle".to_string())),
                                Box::new(Expr::Literal(Literal::Int(360))),
                            )],
                        )))),
                    },
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Bool(false)),
                        body: Box::new(Expr::Ident("angle".to_string())),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(normalize.clone()));
        ctx.fn_defs.push(normalize);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected negative-guarded Int ascent recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = out
            .files
            .iter()
            .find_map(|(name, content)| (name == "Verify_mode.lean").then_some(content))
            .expect("expected generated Lean file");
        assert!(lean.contains("def normalize__fuel"));
        assert!(lean.contains("normalize__fuel ((Int.natAbs angle) + 1) angle"));
    }

    #[test]
    fn proof_mode_accepts_single_list_structural_recursion() {
        let mut ctx = empty_ctx();
        let len = FnDef {
            name: "len".to_string(),
            line: 1,
            params: vec![("xs".to_string(), "List<Int>".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::Ident("xs".to_string())),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::EmptyList,
                        body: Box::new(Expr::Literal(Literal::Int(0))),
                    },
                    MatchArm {
                        pattern: Pattern::Cons("h".to_string(), "t".to_string()),
                        body: Box::new(Expr::TailCall(Box::new((
                            "len".to_string(),
                            vec![Expr::Ident("t".to_string())],
                        )))),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(len.clone()));
        ctx.fn_defs.push(len);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected List structural recursion to be accepted, got: {:?}",
            issues
        );
    }

    #[test]
    fn proof_mode_accepts_single_list_structural_recursion_on_nonfirst_param() {
        let mut ctx = empty_ctx();
        let len_from = FnDef {
            name: "lenFrom".to_string(),
            line: 1,
            params: vec![
                ("count".to_string(), "Int".to_string()),
                ("xs".to_string(), "List<Int>".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::Ident("xs".to_string())),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::EmptyList,
                        body: Box::new(Expr::Ident("count".to_string())),
                    },
                    MatchArm {
                        pattern: Pattern::Cons("h".to_string(), "t".to_string()),
                        body: Box::new(Expr::TailCall(Box::new((
                            "lenFrom".to_string(),
                            vec![
                                Expr::BinOp(
                                    BinOp::Add,
                                    Box::new(Expr::Ident("count".to_string())),
                                    Box::new(Expr::Literal(Literal::Int(1))),
                                ),
                                Expr::Ident("t".to_string()),
                            ],
                        )))),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(len_from.clone()));
        ctx.fn_defs.push(len_from);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected non-first List structural recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("termination_by xs.length"));
        assert!(!lean.contains("partial def lenFrom"));
    }

    #[test]
    fn proof_mode_accepts_single_string_pos_advance_recursion() {
        let mut ctx = empty_ctx();
        let skip_ws = FnDef {
            name: "skipWs".to_string(),
            line: 1,
            params: vec![
                ("s".to_string(), "String".to_string()),
                ("pos".to_string(), "Int".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::FnCall(
                    Box::new(Expr::Attr(
                        Box::new(Expr::Ident("String".to_string())),
                        "charAt".to_string(),
                    )),
                    vec![Expr::Ident("s".to_string()), Expr::Ident("pos".to_string())],
                )),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Constructor("Option.None".to_string(), vec![]),
                        body: Box::new(Expr::Ident("pos".to_string())),
                    },
                    MatchArm {
                        pattern: Pattern::Wildcard,
                        body: Box::new(Expr::TailCall(Box::new((
                            "skipWs".to_string(),
                            vec![
                                Expr::Ident("s".to_string()),
                                Expr::BinOp(
                                    BinOp::Add,
                                    Box::new(Expr::Ident("pos".to_string())),
                                    Box::new(Expr::Literal(Literal::Int(1))),
                                ),
                            ],
                        )))),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(skip_ws.clone()));
        ctx.fn_defs.push(skip_ws);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected String+pos recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("def skipWs__fuel"));
        assert!(!lean.contains("partial def skipWs"));
    }

    #[test]
    fn proof_mode_accepts_mutual_int_countdown_recursion() {
        let mut ctx = empty_ctx();
        let even = FnDef {
            name: "even".to_string(),
            line: 1,
            params: vec![("n".to_string(), "Int".to_string())],
            return_type: "Bool".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::Ident("n".to_string())),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Int(0)),
                        body: Box::new(Expr::Literal(Literal::Bool(true))),
                    },
                    MatchArm {
                        pattern: Pattern::Wildcard,
                        body: Box::new(Expr::TailCall(Box::new((
                            "odd".to_string(),
                            vec![Expr::BinOp(
                                BinOp::Sub,
                                Box::new(Expr::Ident("n".to_string())),
                                Box::new(Expr::Literal(Literal::Int(1))),
                            )],
                        )))),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        let odd = FnDef {
            name: "odd".to_string(),
            line: 2,
            params: vec![("n".to_string(), "Int".to_string())],
            return_type: "Bool".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::Ident("n".to_string())),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Int(0)),
                        body: Box::new(Expr::Literal(Literal::Bool(false))),
                    },
                    MatchArm {
                        pattern: Pattern::Wildcard,
                        body: Box::new(Expr::TailCall(Box::new((
                            "even".to_string(),
                            vec![Expr::BinOp(
                                BinOp::Sub,
                                Box::new(Expr::Ident("n".to_string())),
                                Box::new(Expr::Literal(Literal::Int(1))),
                            )],
                        )))),
                    },
                ],
                line: 2,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(even.clone()));
        ctx.items.push(TopLevel::FnDef(odd.clone()));
        ctx.fn_defs.push(even);
        ctx.fn_defs.push(odd);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected mutual Int countdown recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("def even__fuel"));
        assert!(lean.contains("def odd__fuel"));
        assert!(lean.contains("def even (n : Int) : Bool :="));
        assert!(lean.contains("even__fuel ((Int.natAbs n) + 1) n"));
    }

    #[test]
    fn proof_mode_accepts_mutual_string_pos_recursion_with_ranked_same_edges() {
        let mut ctx = empty_ctx();
        let f = FnDef {
            name: "f".to_string(),
            line: 1,
            params: vec![
                ("s".to_string(), "String".to_string()),
                ("pos".to_string(), "Int".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::BinOp(
                    BinOp::Gte,
                    Box::new(Expr::Ident("pos".to_string())),
                    Box::new(Expr::Literal(Literal::Int(3))),
                )),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Bool(true)),
                        body: Box::new(Expr::Ident("pos".to_string())),
                    },
                    MatchArm {
                        pattern: Pattern::Wildcard,
                        body: Box::new(Expr::TailCall(Box::new((
                            "g".to_string(),
                            vec![Expr::Ident("s".to_string()), Expr::Ident("pos".to_string())],
                        )))),
                    },
                ],
                line: 1,
            })),
            resolution: None,
        };
        let g = FnDef {
            name: "g".to_string(),
            line: 2,
            params: vec![
                ("s".to_string(), "String".to_string()),
                ("pos".to_string(), "Int".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::BinOp(
                    BinOp::Gte,
                    Box::new(Expr::Ident("pos".to_string())),
                    Box::new(Expr::Literal(Literal::Int(3))),
                )),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::Literal(Literal::Bool(true)),
                        body: Box::new(Expr::Ident("pos".to_string())),
                    },
                    MatchArm {
                        pattern: Pattern::Wildcard,
                        body: Box::new(Expr::TailCall(Box::new((
                            "f".to_string(),
                            vec![
                                Expr::Ident("s".to_string()),
                                Expr::BinOp(
                                    BinOp::Add,
                                    Box::new(Expr::Ident("pos".to_string())),
                                    Box::new(Expr::Literal(Literal::Int(1))),
                                ),
                            ],
                        )))),
                    },
                ],
                line: 2,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(f.clone()));
        ctx.items.push(TopLevel::FnDef(g.clone()));
        ctx.fn_defs.push(f);
        ctx.fn_defs.push(g);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected mutual String+pos recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("def f__fuel"));
        assert!(lean.contains("def g__fuel"));
        assert!(!lean.contains("partial def f"));
    }

    #[test]
    fn proof_mode_accepts_mutual_ranked_sizeof_recursion() {
        let mut ctx = empty_ctx();
        let f = FnDef {
            name: "f".to_string(),
            line: 1,
            params: vec![("xs".to_string(), "List<Int>".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::TailCall(Box::new((
                "g".to_string(),
                vec![
                    Expr::Literal(Literal::Str("acc".to_string())),
                    Expr::Ident("xs".to_string()),
                ],
            ))))),
            resolution: None,
        };
        let g = FnDef {
            name: "g".to_string(),
            line: 2,
            params: vec![
                ("acc".to_string(), "String".to_string()),
                ("xs".to_string(), "List<Int>".to_string()),
            ],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::Match {
                subject: Box::new(Expr::Ident("xs".to_string())),
                arms: vec![
                    MatchArm {
                        pattern: Pattern::EmptyList,
                        body: Box::new(Expr::Literal(Literal::Int(0))),
                    },
                    MatchArm {
                        pattern: Pattern::Cons("h".to_string(), "t".to_string()),
                        body: Box::new(Expr::TailCall(Box::new((
                            "f".to_string(),
                            vec![Expr::Ident("t".to_string())],
                        )))),
                    },
                ],
                line: 2,
            })),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(f.clone()));
        ctx.items.push(TopLevel::FnDef(g.clone()));
        ctx.fn_defs.push(f);
        ctx.fn_defs.push(g);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected mutual ranked-sizeOf recursion to be accepted, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("mutual"));
        assert!(lean.contains("def f__fuel"));
        assert!(lean.contains("def g__fuel"));
        assert!(!lean.contains("partial def f"));
        assert!(!lean.contains("partial def g"));
    }

    #[test]
    fn proof_mode_rejects_recursive_pure_functions() {
        let mut ctx = empty_ctx();
        let recursive_fn = FnDef {
            name: "loop".to_string(),
            line: 1,
            params: vec![("n".to_string(), "Int".to_string())],
            return_type: "Int".to_string(),
            effects: vec![],
            desc: None,
            body: Rc::new(FnBody::from_expr(Expr::FnCall(
                Box::new(Expr::Ident("loop".to_string())),
                vec![Expr::Ident("n".to_string())],
            ))),
            resolution: None,
        };
        ctx.items.push(TopLevel::FnDef(recursive_fn.clone()));
        ctx.fn_defs.push(recursive_fn);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.iter().any(|i| i.contains("outside proof subset")),
            "expected recursive function blocker, got: {:?}",
            issues
        );
    }

    #[test]
    fn proof_mode_allows_recursive_types() {
        let mut ctx = empty_ctx();
        let recursive_type = TypeDef::Sum {
            name: "Node".to_string(),
            variants: vec![TypeVariant {
                name: "Cons".to_string(),
                fields: vec!["Node".to_string()],
            }],
            line: 1,
        };
        ctx.items.push(TopLevel::TypeDef(recursive_type.clone()));
        ctx.type_defs.push(recursive_type);

        let issues = proof_mode_issues(&ctx);
        assert!(
            issues
                .iter()
                .all(|i| !i.contains("recursive types require unsafe DecidableEq shim")),
            "did not expect recursive type blocker, got: {:?}",
            issues
        );
    }

    #[test]
    fn law_auto_example_exports_real_proof_artifacts() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/formal/law_auto.av"),
            "law_auto",
        );
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("theorem add_law_commutative :"));
        assert!(lean.contains("theorem id'_law_reflexive : ∀ (x : Int), x = x := by"));
        assert!(lean.contains("theorem incCount_law_keyPresent :"));
        assert!(lean.contains("AverMap.has_set_self"));
        assert!(lean.contains("theorem add_law_commutative_sample_1 :"));
        assert!(lean.contains(":= by native_decide"));
    }

    #[test]
    fn json_example_stays_inside_proof_subset() {
        let ctx = ctx_from_source(include_str!("../../../examples/data/json.av"), "json");
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected json example to stay inside proof subset, got: {:?}",
            issues
        );
    }

    #[test]
    fn json_example_uses_total_defs_and_domain_guarded_laws_in_proof_mode() {
        let ctx = ctx_from_source(include_str!("../../../examples/data/json.av"), "json");
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        assert!(!lean.contains("partial def"));
        assert!(lean.contains("def skipWs__fuel"));
        assert!(lean.contains("def parseValue__fuel"));
        assert!(lean.contains("def toString' (j : Json) : String :="));
        assert!(
            lean.contains(
                "def averMeasureJsonEntries_String (items : List (String × Json)) : Nat :="
            )
        );
        assert!(lean.contains(
            "| .jsonObject x0 => (averMeasureJsonEntries_String (AverMap.entries x0)) + 1"
        ));
        assert!(lean.contains("-- when jsonRoundtripSafe j"));
        assert!(!lean.contains("-- hint: verify law '"));
        assert!(!lean.contains("private theorem toString'_law_parseRoundtrip_aux"));
        assert!(
            lean.contains(
                "theorem toString'_law_parseRoundtrip : ∀ (j : Json), j = Json.jsonNull ∨"
            )
        );
        assert!(lean.contains(
            "jsonRoundtripSafe j = true -> fromString (toString' j) = Except.ok j := by"
        ));
        assert!(
            lean.contains("theorem finishFloat_law_fromCanonicalFloat : ∀ (f : Float), f = 3.5 ∨")
        );
        assert!(lean.contains("theorem finishInt_law_fromCanonicalInt_checked_domain :"));
        assert!(lean.contains(
            "theorem toString'_law_parseValueRoundtrip : ∀ (j : Json), j = Json.jsonNull ∨"
        ));
        assert!(lean.contains("theorem toString'_law_parseRoundtrip_sample_1 :"));
        assert!(lean.contains(
            "example : fromString \"null\" = Except.ok Json.jsonNull := by native_decide"
        ));
    }

    #[test]
    fn transpile_injects_builtin_network_types_and_vector_get_support() {
        let ctx = ctx_from_source(
            r#"
fn firstOrMissing(xs: Vector<String>) -> Result<String, String>
    Option.toResult(Vector.get(xs, 0), "missing")

fn defaultHeader() -> Header
    Header(name = "Content-Type", value = "application/json")

fn mkResponse(body: String) -> HttpResponse
    HttpResponse(status = 200, body = body, headers = [defaultHeader()])

fn requestPath(req: HttpRequest) -> String
    req.path

fn connPort(conn: Tcp.Connection) -> Int
    conn.port
"#,
            "network_helpers",
        );
        let out = transpile(&ctx);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("structure Header where"));
        assert!(lean.contains("structure HttpResponse where"));
        assert!(lean.contains("structure HttpRequest where"));
        assert!(lean.contains("structure Tcp_Connection where"));
        assert!(lean.contains("port : Int"));
    }

    #[test]
    fn law_auto_example_has_no_sorry_in_proof_mode() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/formal/law_auto.av"),
            "law_auto",
        );
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(
            !lean.contains("sorry"),
            "expected law_auto proof export to avoid sorry, got:\n{}",
            lean
        );
    }

    #[test]
    fn map_example_has_no_sorry_in_proof_mode() {
        let ctx = ctx_from_source(include_str!("../../../examples/data/map.av"), "map");
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected map example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        // After codegen change: universal theorems that can't be auto-proved get sorry
        assert!(lean.contains("theorem incCount_law_trackedCountStepsByOne :"));
        assert!(lean.contains("sorry"));
        // Universal theorems that can't be auto-proved now get sorry instead of being omitted
        assert!(lean.contains("theorem countWords_law_presenceMatchesContains_sample_1 :"));
        assert!(lean.contains("theorem countWords_law_trackedWordCount_sample_1 :"));
        assert!(lean.contains("AverMap.has_set_self"));
        assert!(lean.contains("AverMap.get_set_self"));
    }

    #[test]
    fn spec_laws_example_has_no_sorry_in_proof_mode() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/formal/spec_laws.av"),
            "spec_laws",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected spec_laws example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(
            !lean.contains("sorry"),
            "expected spec_laws proof export to avoid sorry, got:\n{}",
            lean
        );
        assert!(lean.contains("theorem absVal_eq_absValSpec :"));
        assert!(lean.contains("theorem clampNonNegative_eq_clampNonNegativeSpec :"));
    }

    #[test]
    fn rle_example_exports_sampled_roundtrip_laws_without_sorry() {
        let ctx = ctx_from_source(include_str!("../../../examples/data/rle.av"), "rle");
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        assert!(
            lean.contains("sorry"),
            "expected rle proof export to contain sorry for unproved universal theorems"
        );
        assert!(lean.contains(
            "theorem encode_law_roundtrip_sample_1 : decode (encode []) = [] := by native_decide"
        ));
        assert!(lean.contains(
            "theorem encodeString_law_string_roundtrip_sample_1 : decodeString (encodeString \"\") = \"\" := by native_decide"
        ));
    }

    #[test]
    fn fibonacci_example_uses_fuelized_int_countdown_in_proof_mode() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/data/fibonacci.av"),
            "fibonacci",
        );
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("def fibTR__fuel"));
        assert!(lean.contains("def fibTR (n : Int) (a : Int) (b : Int) : Int :="));
        assert!(lean.contains("fibTR__fuel ((Int.natAbs n) + 1) n a b"));
        assert!(!lean.contains("partial def fibTR"));
    }

    #[test]
    fn fibonacci_example_stays_inside_proof_subset() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/data/fibonacci.av"),
            "fibonacci",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected fibonacci example to stay inside proof subset, got: {:?}",
            issues
        );
    }

    #[test]
    fn fibonacci_example_matches_general_linear_recurrence_shapes() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/data/fibonacci.av"),
            "fibonacci",
        );
        let fib = ctx.fn_defs.iter().find(|fd| fd.name == "fib").unwrap();
        let fib_tr = ctx.fn_defs.iter().find(|fd| fd.name == "fibTR").unwrap();
        let fib_spec = ctx.fn_defs.iter().find(|fd| fd.name == "fibSpec").unwrap();

        assert!(recurrence::detect_tailrec_int_linear_pair_wrapper(fib).is_some());
        assert!(recurrence::detect_tailrec_int_linear_pair_worker(fib_tr).is_some());
        assert!(recurrence::detect_second_order_int_linear_recurrence(fib_spec).is_some());
    }

    #[test]
    fn fibonacci_example_auto_proves_general_linear_recurrence_spec_law() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/data/fibonacci.av"),
            "fibonacci",
        );
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        assert!(lean.contains("private def fibSpec__nat : Nat -> Int"));
        assert!(!lean.contains("partial def fibSpec"));
        assert!(lean.contains("private theorem fib_eq_fibSpec__worker_nat_shift"));
        assert!(lean.contains("private theorem fib_eq_fibSpec__helper_nat"));
        assert!(lean.contains("private theorem fib_eq_fibSpec__helper_seed"));
        assert!(lean.contains("theorem fib_eq_fibSpec : ∀ (n : Int), fib n = fibSpec n := by"));
        assert!(!lean.contains(
            "-- universal theorem fib_eq_fibSpec omitted: sampled law shape is not auto-proved yet"
        ));
    }

    #[test]
    fn pell_like_example_auto_proves_same_general_shape() {
        let ctx = ctx_from_source(
            r#"
module Pell
    intent =
        "linear recurrence probe"

fn pellTR(n: Int, a: Int, b: Int) -> Int
    match n
        0 -> a
        _ -> pellTR(n - 1, b, a + 2 * b)

fn pell(n: Int) -> Int
    match n < 0
        true -> 0
        false -> pellTR(n, 0, 1)

fn pellSpec(n: Int) -> Int
    match n < 0
        true -> 0
        false -> match n
            0 -> 0
            1 -> 1
            _ -> pellSpec(n - 2) + 2 * pellSpec(n - 1)

verify pell law pellSpec
    given n: Int = [0, 1, 2, 3]
    pell(n) => pellSpec(n)
"#,
            "pell",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected pell example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("private def pellSpec__nat : Nat -> Int"));
        assert!(lean.contains("private theorem pell_eq_pellSpec__worker_nat_shift"));
        assert!(lean.contains("theorem pell_eq_pellSpec : ∀ (n : Int), pell n = pellSpec n := by"));
        assert!(!lean.contains(
            "-- universal theorem pell_eq_pellSpec omitted: sampled law shape is not auto-proved yet"
        ));
    }

    #[test]
    fn nonlinear_pair_state_recurrence_is_not_auto_proved_as_linear_shape() {
        let ctx = ctx_from_source(
            r#"
module WeirdRec
    intent =
        "reject nonlinear pair-state recurrence from linear recurrence prover"

fn weirdTR(n: Int, a: Int, b: Int) -> Int
    match n
        0 -> a
        _ -> weirdTR(n - 1, b, a * b)

fn weird(n: Int) -> Int
    match n < 0
        true -> 0
        false -> weirdTR(n, 0, 1)

fn weirdSpec(n: Int) -> Int
    match n < 0
        true -> 0
        false -> match n
            0 -> 0
            1 -> 1
            _ -> weirdSpec(n - 1) * weirdSpec(n - 2)

verify weird law weirdSpec
    given n: Int = [0, 1, 2, 3]
    weird(n) => weirdSpec(n)
"#,
            "weirdrec",
        );
        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);

        // After codegen change: emit sorry instead of omitting universal theorems
        assert!(lean.contains("sorry"));
        assert!(!lean.contains("private theorem weird_eq_weirdSpec__worker_nat_shift"));
        assert!(lean.contains("theorem weird_eq_weirdSpec_sample_1 :"));
    }

    #[test]
    fn date_example_stays_inside_proof_subset() {
        let ctx = ctx_from_source(include_str!("../../../examples/data/date.av"), "date");
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected date example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(!lean.contains("partial def"));
        assert!(lean.contains("def parseIntSlice (s : String) (from' : Int) (to : Int) : Int :="));
    }

    #[test]
    fn temperature_example_stays_inside_proof_subset() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/core/temperature.av"),
            "temperature",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected temperature example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(!lean.contains("partial def"));
        assert!(
            lean.contains("example : celsiusToFahr 0.0 = 32.0 := by native_decide"),
            "expected verify examples to survive proof export, got:\n{}",
            lean
        );
    }

    #[test]
    fn quicksort_example_stays_inside_proof_subset() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/data/quicksort.av"),
            "quicksort",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected quicksort example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("def isOrderedFrom"));
        assert!(!lean.contains("partial def isOrderedFrom"));
        assert!(lean.contains("termination_by xs.length"));
    }

    #[test]
    fn grok_s_language_example_uses_total_ranked_sizeof_mutual_recursion() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/core/grok_s_language.av"),
            "grok_s_language",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected grok_s_language example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("mutual"));
        assert!(lean.contains("def eval__fuel"));
        assert!(lean.contains("def parseListItems__fuel"));
        assert!(!lean.contains("partial def eval"));
        assert!(!lean.contains("termination_by (sizeOf e,"));
        assert!(lean.contains("-- when validSymbolNames e"));
        assert!(!lean.contains("private theorem toString'_law_parseRoundtrip_aux"));
        assert!(lean.contains(
            "theorem toString'_law_parseRoundtrip : ∀ (e : Sexpr), e = Sexpr.atomNum 42 ∨"
        ));
        assert!(
            lean.contains("validSymbolNames e = true -> parse (toString' e) = Except.ok e := by")
        );
        assert!(lean.contains("theorem toString'_law_parseSexprRoundtrip :"));
        assert!(lean.contains("theorem toString'_law_parseRoundtrip_sample_1 :"));
    }

    #[test]
    fn lambda_example_keeps_only_eval_outside_proof_subset() {
        let ctx = ctx_from_source(include_str!("../../../examples/core/lambda.av"), "lambda");
        let issues = proof_mode_issues(&ctx);
        assert_eq!(
            issues,
            vec!["recursive function 'eval' is outside proof subset (currently supported: Int countdown, second-order affine Int recurrences with pair-state worker, structural recursion on List/recursive ADTs, String+position, mutual Int countdown, mutual String+position, and ranked sizeOf recursion)".to_string()]
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("def termToString__fuel"));
        assert!(lean.contains("def subst__fuel"));
        assert!(lean.contains("def countS__fuel"));
        assert!(!lean.contains("partial def termToString"));
        assert!(!lean.contains("partial def subst"));
        assert!(!lean.contains("partial def countS"));
        assert!(lean.contains("partial def eval"));
    }

    #[test]
    fn mission_control_example_stays_inside_proof_subset() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/apps/mission_control.av"),
            "mission_control",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected mission_control example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(!lean.contains("partial def normalizeAngle"));
        assert!(lean.contains("def normalizeAngle__fuel"));
    }

    #[test]
    fn notepad_store_example_stays_inside_proof_subset() {
        let ctx = ctx_from_source(
            include_str!("../../../examples/apps/notepad/store.av"),
            "notepad_store",
        );
        let issues = proof_mode_issues(&ctx);
        assert!(
            issues.is_empty(),
            "expected notepad/store example to stay inside proof subset, got: {:?}",
            issues
        );

        let out = transpile_for_proof_mode(&ctx, VerifyEmitMode::NativeDecide);
        let lean = generated_lean_file(&out);
        assert!(lean.contains("def deserializeLine (line : String) : Except String Note :="));
        assert!(lean.contains("Except String (List Note)"));
        assert!(!lean.contains("partial def deserializeLine"));
        assert!(lean.contains("-- when noteRoundtripSafe note"));
        assert!(lean.contains("-- when notesRoundtripSafe notes"));
        assert!(lean.contains(
            "theorem serializeLine_law_lineRoundtrip : ∀ (note : Note), note = { id' := 1, title := \"Hello\", body := \"World\" : Note } ∨"
        ));
        assert!(lean.contains(
            "theorem serializeLines_law_notesRoundtrip : ∀ (notes : List Note), notes = [] ∨"
        ));
        assert!(lean.contains("notesRoundtripSafe notes = true ->"));
        assert!(lean.contains("parseNotes (s!\"{String.intercalate \"\\n\" (serializeLines notes)}\\n\") = Except.ok notes"));
        assert!(lean.contains("theorem serializeLine_law_lineRoundtrip_sample_1 :"));
        assert!(lean.contains("theorem serializeLines_law_notesRoundtrip_sample_1 :"));
    }
}