fix(conv): check operator type-arguments in applied op-convertibility - #1094
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fix(conv): check operator type-arguments in applied op-convertibility#1094namasikanam wants to merge 1 commit into
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The `Fapp(Fop(p1,_), _), Fapp(Fop(p2,_), _)` shortcut in `conv` (ecReduction.ml) treated two applications of the same operator path as convertible without comparing their type-argument lists. When the type parameter is "phantom" (present in the operator's definition but reducing out of its head arrow type), distinct instantiations were wrongly declared equal. This is unsound: `reflexivity` proves wrap<:bool> 0 = wrap<:unit> 0 for `op wrap ['a] (x:int):int = size (to_seq<:'a> predT)`, while the stdlib pins those to |bool|=2 and |unit|=1 — yielding a proof of `false` with no axioms. The fix mirrors the unapplied `Fop, Fop` case (a few lines above) and `is_alpha_eq`, both of which already check `List.all2 for_type`. The change only makes conversion stricter (on a type-arg mismatch it falls through to the general head-conversion / unfolding path), so it cannot introduce new conversions; genuinely-true phantom equations still convert via unfolding. Adds tests/conv-typeargs.ec, a regression test using `fail reflexivity`: it compiles once the bug is fixed and fails to compile if it regresses. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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A soundness bug found by Claude Code. When checking equivalence of two operators, the types of arguments should also be checked. This does not make difference when the operators are not generic, but it does make difference for generic operators.