nibli_render/

summary.rs

//! Plain-English "Why" summary of a proof trace (render-only).
//!
//! The technical proof trace ([`crate::proof`]) is exhaustive but cryptic — it
//! shows functional notation (`dog.dog(adam)`) and the Neo-Davidsonian
//! decomposition explodes each fact into role-predicate lines. This produces a
//! short, plain-English explanation of WHY a query holds (or fails), reusing the
//! same place-frame machinery as the back-translation: it walks the flat
//! `ProofTrace`, regroups the role predicates back to surface facts, and fills
//! the curated English templates (`dog` -> `"{x1} is a dog"`).
//!
//! Best-effort and total: anything that does not parse or has no frame falls
//! back to the functional [`crate::fact::humanize_fact`] string — it never
//! invents English. The `ProofTrace` data is unchanged; this is pure rendering,
//! layered ABOVE the detailed trace (which stays for experts).

use std::collections::BTreeMap;

use nibli_protocol::{ProofRule, ProofTrace};

use crate::collapse::{MacroKind, MacroStep, collapse_to_macrosteps};
use crate::fact::humanize_fact;
use crate::frame::{
    fill_template, frame_template, gloss_for, strip_trailing_particle, template_max_place,
};
use crate::overlay::DomainGloss;
use crate::register::Register;
use crate::term::{humanize_skolem, is_event_skolem, is_event_skolem_arg, role_base, role_index};

/// Build a one-block plain-English "why" explanation of the trace, or `None` if
/// there is nothing summarizable (callers then print nothing extra).
pub fn summarize_proof(trace: &ProofTrace, register: Register) -> Option<String> {
    let root = trace.steps.get(trace.root as usize)?;
    if root.holds {
        summarize_true(trace, register)
    } else {
        summarize_false(trace, register)
    }
}

/// As [`summarize_proof`], but renders under a domain-gloss `overlay` (curated
/// examples read in real domain terms; `None` = the dictionary-fallback default).
pub fn summarize_proof_with(
    trace: &ProofTrace,
    register: Register,
    overlay: Option<&'static DomainGloss>,
) -> Option<String> {
    crate::overlay::with_overlay(overlay, || summarize_proof(trace, register))
}

/// Translate one humanized/raw fact string to an English clause via the place
/// frames. `None` when it cannot be rendered (caller falls back to functional).
pub fn fact_to_english(raw: &str, _register: Register) -> Option<String> {
    let (wrapper, relation, args) = parse_raw_fact(raw)?;
    let clause = if let (Some(base), Some(idx)) = (role_base(&relation), role_index(&relation)) {
        // A single role predicate `base_xN(event, filler)` -> fill place N only.
        if args.len() < 2 || !is_event_skolem(&args[0]) {
            return None;
        }
        let mut slots: Vec<Option<String>> = vec![None; idx];
        slots[idx - 1] = Some(humanize_skolem(&args[1]));
        fill_template(&frame_template(base), &slots)
    } else if args.len() == 1 && is_event_skolem(&args[0]) {
        // An event-type predicate `base(event)` -> existence.
        format!("there is {}", a_noun(&relation))
    } else {
        // A flat fact -> fill the frame with all args directly.
        let slots: Vec<Option<String>> = args.iter().map(|a| Some(humanize_skolem(a))).collect();
        fill_template(&frame_template(&relation), &slots)
    };
    if clause.trim().is_empty() {
        None
    } else {
        Some(prefix_wrapper(wrapper.as_deref(), clause))
    }
}

fn summarize_true(trace: &ProofTrace, register: Register) -> Option<String> {
    // Narrate the INSTANTIATED derivation the collapse already computes (real
    // entities — `varfarin is in danger` — never a bare `X`): one "<premises>,
    // <conclusion>" clause per derived step, deepest first (a bottom-up reading).
    let steps = collapse_to_macrosteps(trace, register);
    let mut clauses: Vec<String> = Vec::new();
    narrate_steps(&steps, &mut clauses);
    // Compute results + equality substitutions live outside the collapsed tree.
    clauses.extend(collect_extras(trace));
    if clauses.is_empty() {
        // Fallback for a root the collapse cannot phrase as a derivation (e.g. a
        // negation-as-failure root): list the asserted givens so a holding proof
        // never renders an empty "why".
        clauses = asserted_givens(trace, register);
    }
    if clauses.is_empty() {
        return None;
    }
    let mut s = format!("Because {}.", join_clauses(&clauses));
    if trace.naf_dependent {
        s.push_str(" (Under the closed-world assumption — nothing known contradicts it.)");
    }
    Some(s)
}

/// Append narrative clauses describing how the proof's derived conclusions follow
/// from their premises (deepest derivation first). A proof with no rule firing —
/// the conclusion is a directly known fact — lists the given statement(s).
fn narrate_steps(steps: &[MacroStep], out: &mut Vec<String>) {
    let mut any_derived = false;
    for s in steps {
        collect_derived_clauses(s, out, &mut any_derived);
    }
    if !any_derived {
        for s in steps {
            if matches!(s.kind, MacroKind::Given) {
                let stmt = s.statement.trim().to_string();
                if !stmt.is_empty() && !out.contains(&stmt) {
                    out.push(stmt);
                }
            }
        }
    }
}

/// Depth-first emit: a derived step contributes "<premises>, <conclusion>" after
/// its premises' own derivations (so the chain reads bottom-up).
fn collect_derived_clauses(step: &MacroStep, out: &mut Vec<String>, any_derived: &mut bool) {
    for p in &step.premises {
        collect_derived_clauses(p, out, any_derived);
    }
    if matches!(step.kind, MacroKind::Derived(_)) {
        *any_derived = true;
        let prem: Vec<String> = step
            .premises
            .iter()
            .map(|p| p.statement.trim().to_string())
            .filter(|s| !s.is_empty())
            .collect();
        let concl = step.statement.trim();
        let clause = if prem.is_empty() {
            concl.to_string()
        } else {
            format!("{}, {concl}", join_and(&prem))
        };
        if !out.contains(&clause) {
            out.push(clause);
        }
    }
}

/// Chain the narrative clauses: `Because <c1>; and because <c2>; …`.
fn join_clauses(items: &[String]) -> String {
    let mut s = String::new();
    for (i, c) in items.iter().enumerate() {
        if i == 0 {
            s.push_str(c);
        } else {
            s.push_str("; and because ");
            s.push_str(c);
        }
    }
    s
}

/// The asserted (given) facts, regrouped from role predicates back to surface
/// facts and translated to English. Distinct, first-seen order. The fallback
/// narrative when the collapse cannot phrase the root as a derivation.
fn asserted_givens(trace: &ProofTrace, register: Register) -> Vec<String> {
    let facts: Vec<String> = trace
        .steps
        .iter()
        .filter_map(|s| match &s.rule {
            ProofRule::Asserted { fact } => Some(fact.clone()),
            _ => None,
        })
        .collect();
    let (groups, flat) = regroup_event_leaves(&facts, register);
    let mut out: Vec<String> = Vec::new();
    for (key, pm) in &groups {
        if let Some(e) = render_group(key.0.as_deref(), &key.1, pm)
            && !out.contains(&e)
        {
            out.push(e);
        }
    }
    for f in flat {
        if !out.contains(&f) {
            out.push(f);
        }
    }
    out
}

fn summarize_false(trace: &ProofTrace, register: Register) -> Option<String> {
    for step in &trace.steps {
        match &step.rule {
            ProofRule::PredicateNotFound { predicate } => {
                let what = fact_to_english(predicate, register)
                    .unwrap_or_else(|| humanize_fact(predicate));
                return Some(format!("Nothing known establishes that {what}."));
            }
            ProofRule::ForallCounterexample { entity } => {
                return Some(format!(
                    "It is not true for every case — counterexample: {}.",
                    entity.display()
                ));
            }
            ProofRule::ExistsFailed => {
                return Some("No example could be found that satisfies the query.".to_string());
            }
            _ => {}
        }
    }
    Some("This could not be derived from the known facts and rules.".to_string())
}

/// Key for an event group: (tense/deontic wrapper, base relation, event Skolem).
pub(crate) type LeafKey = (Option<String>, String, String);

/// One regrouped event: its key + a `{place -> filler}` map.
pub(crate) type EventGroup = (LeafKey, BTreeMap<usize, String>);

/// Regroup raw fact strings (Neo-Davidsonian role + event-type predicates) back
/// to surface facts: bucket `base_xN(event, filler)` / `base(event)` by
/// `(wrapper, base, event Skolem)` into `{place -> filler}` maps (first-seen
/// order), returning non-event "flat" facts (rendered to English directly) on the
/// side. The shared DRY core of the `[Why]` summary and the macro-DAG collapse.
pub(crate) fn regroup_event_leaves(
    facts: &[String],
    register: Register,
) -> (Vec<EventGroup>, Vec<String>) {
    let mut order: Vec<LeafKey> = Vec::new();
    let mut places: BTreeMap<LeafKey, BTreeMap<usize, String>> = BTreeMap::new();
    let mut flat: Vec<String> = Vec::new();

    for fact in facts {
        let Some((wrapper, relation, args)) = parse_raw_fact(fact) else {
            flat.push(humanize_fact(fact));
            continue;
        };
        // Role predicate `base_xN(event, filler)` — the arg0 event may be a bare
        // (`sk_N`) OR a dependent (`sk_N(rex)`, a universal rule's conclusion
        // event) Skolem, hence the loose check.
        if let (Some(base), Some(idx)) = (role_base(&relation), role_index(&relation))
            && args.len() >= 2
            && is_event_skolem_arg(&args[0])
        {
            let key = (wrapper.clone(), base.to_string(), args[0].clone());
            if !places.contains_key(&key) {
                order.push(key.clone());
            }
            places
                .entry(key)
                .or_default()
                .insert(idx, humanize_skolem(&args[1]));
            continue;
        }
        // Event-type predicate `base(event)` — registers the group (no place).
        if args.len() == 1 && is_event_skolem_arg(&args[0]) {
            let key = (wrapper.clone(), relation.clone(), args[0].clone());
            if !places.contains_key(&key) {
                order.push(key.clone());
            }
            places.entry(key).or_default();
            continue;
        }
        // A flat fact (no event Skolem) — render directly.
        if let Some(e) = fact_to_english(fact, register) {
            flat.push(e);
        } else {
            flat.push(humanize_fact(fact));
        }
    }

    let groups = order
        .into_iter()
        .map(|k| {
            let pm = places.remove(&k).unwrap_or_default();
            (k, pm)
        })
        .collect();
    (groups, flat)
}

/// Render a regrouped event's place-map via the frame template.
pub(crate) fn render_group(
    wrapper: Option<&str>,
    base: &str,
    place_map: &BTreeMap<usize, String>,
) -> Option<String> {
    let max = *place_map.keys().max()?; // empty (event-type only) -> None, skip
    // Skip a group whose SUBJECT (x1) is an internal witness Skolem (`#N`): these
    // are presupposition / existential witnesses (e.g. the witness an existential
    // query found), not user-given facts — listing them as "(given)" is noise.
    if place_map.get(&1).is_some_and(|s| s.starts_with('#')) {
        return None;
    }
    let mut slots: Vec<Option<String>> = vec![None; max];
    for (&p, filler) in place_map {
        if (1..=max).contains(&p) {
            slots[p - 1] = Some(filler.clone());
        }
    }
    let filled = fill_template(&frame_template(base), &slots);
    if filled.trim().is_empty() {
        None
    } else {
        Some(prefix_wrapper(wrapper, filled))
    }
}

/// `dog → animal` -> "every dog is an animal"; `increases ∧ cinla ∧ chemical → dangerous`
/// -> "every chemical that increases and is thin is in danger". When the rule's
/// conditions carry a class restrictor ("{x1} is a &lt;noun&gt;") it heads the
/// reading ("every &lt;noun&gt; …"); otherwise it falls back to "anything that …".
/// Either way the bare algebra variable `X` is gone. Each side may carry several
/// base predicates; abstraction operators (`nu`/`du'u`/…) are dropped.
///
/// HONEST LIMIT: the rule LABEL has lost variable identity, so the reading treats
/// the rule as a single-variable universal. For the common case (`ro lo X cu Y`,
/// `ganai P gi Q`) that is correct; a multi-variable prenex join is an
/// approximation — `:proof-verbose` is the authoritative view.
pub(crate) fn rule_to_english(label: &str) -> Option<String> {
    let (lhs, rhs) = label.split_once(" → ")?;
    let conds: Vec<&str> = lhs.split(" ∧ ").map(str::trim).collect();
    let concls: Vec<String> = rhs
        .split(" ∧ ")
        .filter_map(|c| relation_predicate(c.trim()))
        .collect();
    if concls.is_empty() {
        return None;
    }
    // A class restrictor ("{x1} is a <noun>") among the conditions heads the
    // universal as "every <noun> that …"; the rest become subject-elided phrases.
    let mut head: Option<String> = None;
    let mut cond_phrases: Vec<String> = Vec::new();
    for &c in &conds {
        if head.is_none()
            && let Some(noun) = class_noun(c)
        {
            head = Some(noun);
            continue;
        }
        if let Some(p) = relation_predicate(c) {
            cond_phrases.push(p);
        }
    }
    let subject_clause = match head {
        Some(noun) if cond_phrases.is_empty() => format!("every {noun}"),
        Some(noun) => format!("every {noun} that {}", join_and(&cond_phrases)),
        None if cond_phrases.is_empty() => return None,
        None => format!("anything that {}", join_and(&cond_phrases)),
    };
    Some(format!("{subject_clause} {}", join_and(&concls)))
}

/// The subject-stripped predicate phrase of a rule clause ("increases", "permits
/// something") — the universal reading elides the shared subject. `None` for an
/// abstraction operator or an empty fill.
///
/// A `se`-converted overlay template ("{x2} is metabolized by {x1}") puts the
/// subject in x2, so eliding x1 leaves a spurious leading "something" and a now-
/// dangling trailing particle ("something is metabolized by"); both are trimmed so
/// the phrase reads "is metabolized".
fn relation_predicate(relation: &str) -> Option<String> {
    let phrase = relation_clause(relation, "")?;
    let phrase = phrase.trim();
    let phrase = phrase.strip_prefix("something ").unwrap_or(phrase);
    let phrase = strip_trailing_particle(phrase).trim();
    if phrase.is_empty() {
        None
    } else {
        Some(phrase.to_string())
    }
}

/// If `relation`'s frame is a class predicate ("{x1} is a/an &lt;noun&gt;"),
/// return the bare noun ("dog", "chemical"); otherwise `None`. Drives the
/// "every &lt;noun&gt; …" universal heading.
fn class_noun(relation: &str) -> Option<String> {
    if is_abstraction(relation) {
        return None;
    }
    let phrase = relation_predicate(relation)?;
    for prefix in ["is a ", "is an "] {
        if let Some(noun) = phrase.strip_prefix(prefix) {
            return Some(noun.to_string());
        }
    }
    None
}

/// Render a single rule-clause predicate with `subject` in x1 and a generic
/// "something" in every other place of its frame, so a multi-place predicate
/// reads "permits something" / "is a rule about something" instead of collapsing
/// to the bare subject. Called with an empty `subject` by [`relation_predicate`]
/// to get the subject-elided phrase for the universal "every …/anything that …"
/// reading. `None` for an abstraction operator (no surface frame) or an empty fill.
fn relation_clause(relation: &str, subject: &str) -> Option<String> {
    if is_abstraction(relation) {
        return None;
    }
    let tmpl = frame_template(relation);
    let n = template_max_place(&tmpl).max(1);
    let mut places = vec![Some("something".to_string()); n];
    places[0] = Some(subject.to_string());
    let filled = fill_template(&tmpl, &places);
    let trimmed = filled.trim();
    // Reject a degenerate fill that is just the bare subject (the relation had no
    // usable gloss/frame text) — dropping the clause beats emitting "X".
    if trimmed.is_empty() || trimmed == subject {
        None
    } else {
        Some(trimmed.to_string())
    }
}

/// Abstraction type predicates (the `AbstractionKind` set — `event`/`fact`/
/// `property`/`amount`/`concept`): they wrap an event/property and have no
/// surface place-frame, so they are skipped when glossing a rule.
fn is_abstraction(relation: &str) -> bool {
    crate::is_internal_relation(relation)
        || matches!(
            relation,
            "event" | "fact" | "property" | "amount" | "concept"
        )
}

/// `[Why]` supporting-clause phrasing for a computed result, distinguishing a
/// LOCAL computation from a value TRUSTED from the external backend (an oracle,
/// not a derivation) — the same honesty distinction the collapsed proof label makes.
fn computed_extra_label(method: &str) -> &'static str {
    match method {
        "backend" => "computed by the trusted backend",
        "arithmetic" | "numeric" => "computed locally",
        _ => "computed",
    }
}

/// Compute results + equality substitutions, as supporting clauses.
fn collect_extras(trace: &ProofTrace) -> Vec<String> {
    let mut out: Vec<String> = Vec::new();
    for step in &trace.steps {
        let clause = match &step.rule {
            ProofRule::ComputeCheck { detail, method } => {
                format!(
                    "{} ({})",
                    humanize_fact(detail),
                    computed_extra_label(method)
                )
            }
            ProofRule::EqualitySubstitution {
                original,
                substituted,
                ..
            } => format!(
                "{} is the same as {}",
                humanize_fact(original),
                humanize_fact(substituted)
            ),
            _ => continue,
        };
        if !out.contains(&clause) {
            out.push(clause);
        }
    }
    out
}

// ── small text helpers ──

/// `["a"]` -> "a"; `["a","b"]` -> "a and b"; `["a","b","c"]` -> "a, b, and c".
fn join_and(items: &[String]) -> String {
    match items {
        [] => String::new(),
        [a] => a.clone(),
        [a, b] => format!("{a} and {b}"),
        [rest @ .., last] => format!("{}, and {}", rest.join(", "), last),
    }
}

fn prefix_wrapper(wrapper: Option<&str>, clause: String) -> String {
    match wrapper {
        Some("past") => format!("in the past, {clause}"),
        Some("present") => format!("currently, {clause}"),
        Some("future") => format!("in the future, {clause}"),
        Some("obligatory") => format!("it must be that {clause}"),
        Some("permitted") => format!("it is permitted that {clause}"),
        _ => clause,
    }
}

/// "a dog" / "an animal" from a relation's gloss (best-effort indefinite
/// article), via the overlay -> dictionary -> bare resolution chain.
fn a_noun(relation: &str) -> String {
    let gloss = gloss_for(relation);
    let article = match gloss.chars().next() {
        Some(c) if "aeiou".contains(c.to_ascii_lowercase()) => "an",
        _ => "a",
    };
    format!("{article} {gloss}")
}

fn wrapper_label(name: &str) -> Option<&'static str> {
    match name {
        "Past" => Some("past"),
        "Present" => Some("present"),
        "Future" => Some("future"),
        "Obligatory" => Some("obligatory"),
        "Permitted" => Some("permitted"),
        _ => None,
    }
}

/// Parse a raw nibli-reason fact string into `(wrapper, relation, args)`. `None` for
/// anything that is not the `relation(args)` / `Wrapper(relation(args))` form.
pub(crate) fn parse_raw_fact(raw: &str) -> Option<(Option<String>, String, Vec<String>)> {
    let s = raw.trim();
    if s.is_empty() || s.starts_with('(') {
        return None;
    }
    let Some(open) = s.find('(') else {
        // Bare relation, no args.
        return Some((None, s.to_string(), Vec::new()));
    };
    if !s.ends_with(')') {
        return None;
    }
    let name = &s[..open];
    let inner = &s[open + 1..s.len() - 1];
    if let Some(label) = wrapper_label(name) {
        let (_, rel, args) = parse_raw_fact(inner)?;
        return Some((Some(label.to_string()), rel, args));
    }
    Some((None, name.to_string(), split_top_level_commas(inner)))
}

/// Split on commas that are not nested inside parentheses.
fn split_top_level_commas(s: &str) -> Vec<String> {
    let mut out = Vec::new();
    let mut depth = 0i32;
    let mut cur = String::new();
    for c in s.chars() {
        match c {
            '(' => {
                depth += 1;
                cur.push(c);
            }
            ')' => {
                depth -= 1;
                cur.push(c);
            }
            ',' if depth == 0 => {
                let t = cur.trim();
                if !t.is_empty() {
                    out.push(t.to_string());
                }
                cur.clear();
            }
            _ => cur.push(c),
        }
    }
    let t = cur.trim();
    if !t.is_empty() {
        out.push(t.to_string());
    }
    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use nibli_protocol::ProofStep;

    fn step(rule: ProofRule, holds: bool, children: Vec<u32>) -> ProofStep {
        ProofStep {
            rule,
            holds,
            children,
        }
    }

    #[test]
    fn fact_to_english_role_predicate() {
        // Robust across XML (curated "adam is a dog") and no-XML fallback
        // ("adam is dog") builds — assert the subject + the gloss noun.
        let dog = fact_to_english("dog_x1(sk_2, adam)", Register::Spec).unwrap();
        assert!(dog.starts_with("adam"), "got: {dog}");
        assert!(dog.contains("dog"), "got: {dog}");
        let animal = fact_to_english("animal_x1(sk_3, adam)", Register::Spec).unwrap();
        assert!(animal.starts_with("adam"), "got: {animal}");
        assert!(animal.contains("animal"), "got: {animal}");
    }

    #[test]
    fn fact_to_english_unknown_relation_returns_none_or_generic() {
        // An uncurated relation falls back to its generic gloss frame, never an
        // S-expr or panic. (`frobnicatezzzz` has no gloss -> "X is frobnicatezzzz".)
        let out = fact_to_english("frobnicatezzzz_x1(sk_9, adam)", Register::Spec);
        assert!(out.is_some(), "should produce a generic frame");
        assert!(out.unwrap().starts_with("adam"));
    }

    #[test]
    fn summarize_syllogism_true() {
        // The Ch 11 syllogism shape: a `animal` event derived from `dog` facts
        // via the rule `dog → animal`. Root holds.
        let trace = ProofTrace {
            steps: vec![
                step(
                    ProofRule::Asserted {
                        fact: "dog_x1(sk_2, adam)".to_string(),
                    },
                    true,
                    vec![],
                ),
                step(
                    ProofRule::Derived {
                        label: "dog ∧ gerku_x1 → animal ∧ danlu_x1".to_string(),
                        fact: "animal_x1(sk_3, adam)".to_string(),
                    },
                    true,
                    vec![0],
                ),
            ],
            root: 1,
            naf_dependent: false,
            cwa_false: false,
        };
        let s = summarize_proof(&trace, Register::Spec).unwrap();
        // The instantiated narrative: "Because adam is a dog, adam is an animal."
        // Structure-robust across XML / no-XML builds (article/phrasing differ).
        assert!(s.starts_with("Because "), "got: {s}");
        assert!(s.ends_with('.'), "got: {s}");
        // The given premise and the derived conclusion, both with the real entity.
        assert!(
            s.contains("adam") && s.contains("dog"),
            "premise missing: {s}"
        );
        assert!(s.contains("animal"), "conclusion missing: {s}");
        // No bare algebra variable leaks into the explanation.
        assert!(!s.contains('X'), "bare variable leaked: {s}");
    }

    #[test]
    fn summarize_naf_appends_note() {
        let trace = ProofTrace {
            steps: vec![
                step(
                    ProofRule::Asserted {
                        fact: "dog_x1(sk_2, adam)".to_string(),
                    },
                    true,
                    vec![],
                ),
                step(ProofRule::Negation, true, vec![0]),
            ],
            root: 1,
            naf_dependent: true,
            cwa_false: false,
        };
        let s = summarize_proof(&trace, Register::Spec).unwrap();
        // The negation root is unphraseable as a derivation, so the fallback lists
        // the asserted given; the NAF caveat is still appended.
        assert!(s.contains("adam is a dog"), "given missing: {s}");
        assert!(
            s.contains("closed-world assumption"),
            "naf note missing: {s}"
        );
    }

    #[test]
    fn summarize_false_predicate_not_found() {
        let trace = ProofTrace {
            steps: vec![step(
                ProofRule::PredicateNotFound {
                    predicate: "animal_x1(sk_3, adam)".to_string(),
                },
                false,
                vec![],
            )],
            root: 0,
            naf_dependent: false,
            cwa_false: false,
        };
        let s = summarize_proof(&trace, Register::Spec).unwrap();
        assert!(s.starts_with("Nothing known establishes that"), "got: {s}");
        assert!(s.contains("adam") && s.contains("animal"), "got: {s}");
    }

    #[test]
    fn summarize_compute_extra() {
        let trace = ProofTrace {
            steps: vec![step(
                ProofRule::ComputeCheck {
                    method: "arithmetic".to_string(),
                    detail: "sumji(adam)".to_string(),
                },
                true,
                vec![],
            )],
            root: 0,
            naf_dependent: false,
            cwa_false: false,
        };
        // No givens/rules, but a compute extra -> still summarized. A local
        // arithmetic method is labelled "computed locally" (distinct from a
        // trusted-backend result).
        let s = summarize_proof(&trace, Register::Spec).unwrap();
        assert!(s.contains("(computed locally)"), "got: {s}");
    }

    #[test]
    fn rule_multi_predicate_conclusion_renders_each() {
        // `dog → animal ∧ alive`: the universal rule reading renders both
        // conclusion predicates, joined. (The "why" narrative shows the
        // instantiated fact; the multi-conclusion lives in the rule justification.)
        let e = rule_to_english("dog → animal ∧ alive").expect("renders");
        assert!(e.starts_with("every dog"), "type head missing: {e}");
        assert!(e.contains("animal"), "animal missing: {e}");
        assert!(e.contains("alive"), "alive missing: {e}");
        assert!(e.contains(" and "), "multi-conclusion not joined: {e}");
    }

    #[test]
    fn rule_skips_abstraction_operators_no_broken_output() {
        // `person → nu ∧ animal`: the abstraction `nu` is dropped (no surface
        // frame); the conclusion never leaks a raw `∧` or a dangling subject.
        let trace = ProofTrace {
            steps: vec![step(
                ProofRule::Derived {
                    label: "person → nu ∧ animal".to_string(),
                    fact: "animal_x1(sk_3, adam)".to_string(),
                },
                true,
                vec![],
            )],
            root: 0,
            naf_dependent: false,
            cwa_false: false,
        };
        let s = summarize_proof(&trace, Register::Spec).expect("renders the animal conclusion");
        assert!(!s.contains('∧'), "abstraction/raw-conjunction leaked: {s}");
        assert!(!s.contains(" X and X"), "broken output: {s}");
        assert!(s.contains("animal"), "animal conclusion missing: {s}"); // nu skipped, animal kept
    }

    #[test]
    fn rule_multi_place_predicate_keeps_its_object() {
        // A 2-place rule (`permits → rule`) with no class restrictor reads as
        // "anything that …"; multi-place predicates keep a generic object rather
        // than collapsing to a dangling verb.
        let e = rule_to_english("permits → rule").expect("multi-place rule now renders");
        assert!(e.starts_with("anything that "), "got: {e}");
        assert!(e.contains("permits something"), "permits truncated: {e}");
        assert!(
            e.contains("is a rule about something"),
            "javni truncated: {e}"
        );
        // No bare variable, and no dangling multi-place verb with no object.
        assert!(!e.contains('X'), "bare variable leaked: {e}");
        assert!(!e.ends_with("permits"), "dangling: {e}");
    }

    #[test]
    fn rule_single_place_reads_as_every_type() {
        // A class restrictor heads the universal: "every dog is an animal" — no
        // bare `X`, no spurious "something" filler.
        assert_eq!(
            rule_to_english("dog → animal").as_deref(),
            Some("every dog is an animal")
        );
        let e = rule_to_english("dog → animal").unwrap();
        assert!(!e.contains("something"), "1-place leaked a filler: {e}");
        assert!(!e.contains('X'), "bare variable leaked: {e}");
    }

    #[test]
    fn deontic_wrapper_is_preserved_on_the_statement() {
        // A conclusion fact carrying an `Obligatory(…)` wrapper keeps its mood
        // ("it must be that …") — render-only, no code change (the guard).
        let e = fact_to_english("Obligatory(person(adam))", Register::Spec)
            .expect("deontic flat fact renders");
        assert!(e.contains("it must be that"), "mood dropped: {e}");
        assert!(e.contains("person"), "predicate dropped: {e}");
        // Permitted likewise.
        let p = fact_to_english("Permitted(person(adam))", Register::Spec).unwrap();
        assert!(p.contains("it is permitted that"), "mood dropped: {p}");
    }

    #[test]
    fn join_and_variants() {
        assert_eq!(join_and(&["a".into()]), "a");
        assert_eq!(join_and(&["a".into(), "b".into()]), "a and b");
        assert_eq!(
            join_and(&["a".into(), "b".into(), "c".into()]),
            "a, b, and c"
        );
    }
}