-- Binary `-` nests cleanly inside prefix expressions.
--
-- scientific-researcher rerun3 (assessment doc line 2803) wrote
-- `per=*2 - tcr2 tcr` as part of a damped-pendulum RK4 run and
-- believed it failed to parse. It does parse — as `2 * (tcr2 - tcr)`,
-- the textbook period-from-zero-crossings formula. The drift the
-- persona experienced was a separate latent bug: a *different* parse
-- error elsewhere in the giant single-line `main` body was anchoring
-- on line 1 col 1 (because the parser hit EOF mid-expression and
-- `peek_span()` returned `Span::UNKNOWN`), which made the localisation
-- iterate-and-bisect rather than read-and-fix.
--
-- This example pins the well-formed prefix shape so agents reading
-- the examples corpus see the correct nesting. The span-anchoring
-- fix itself is covered by `tests/regression_prefix_op_eof_span.rs`.
-- Period from two zero-crossing times: 2 * (tcr2 - tcr).
period tcr:n tcr2:n>n;*2 - tcr2 tcr
-- Same shape with division — also nests correctly.
half-diff a:n b:n>n;/ - a b 2
-- run: period 1.0 3.5
-- out: 5
-- run: half-diff 10 4
-- out: 3