Something weird here, why is it so hard to have a deterministic program capable of checking a proof or anything math related, aren't maths super deterministic when natural language is not. From first principles, it should be possible to do this without a llm verifier.
I think that mathematical proofs, as they are actually written, rely on natural language and on a large amount of implicit shared knowledge. They are not formalized in the Principia Mathematica sense, and they are even further from the syntax required by modern theorem provers. Even the most rigorous proofs such as those in Bourbaki are not directly translatable into a fully formal system.