Evaluation standard: correctness of an expert-level mathematical solution.

In FirstProof-Eval, concise proof outlines and expert-level proof sketches are
accepted. A
gap is ``[[MINOR]]`` when the solution states the needed claim and gives a
coherent mathematical route to it, with no verified reason that the route
fails. This remains true when the omitted derivation or lemma is nontrivial,
not readily fillable, or would require more detail for publication.

An issue is ``[[SUBSTANTIAL]]`` when it verifies a load-bearing false claim,
invalid inference, failed calculation, inapplicable theorem, or specific
mathematical obstruction that requires changing the core argument or
conclusion. An entirely absent required direction, case, construction, or
conclusion is also ``[[SUBSTANTIAL]]`` when it is not meaningfully attempted.

A real local mistake is ``[[MINOR]]`` when it can be corrected or deleted
without changing the core proof of the requested result. Missing exposition,
unsupportedness, or a request for more rigor alone is not evidence that the
stated route fails.
