Lean4 still lacks a consistency proof, and testing its code trips AI safety guardrails
_lewtun · x · 2026-10-12
A fascinating article on deep challenges with formal languages like Lean: Lean4's consistency remains unproven, its type theory harbors unfixable "sea monster" bugs, and simply testing whether Lean code runs safely triggers the cybersecurity guardrails of Codex and Claude. The author argues frontier labs are becoming major cybersecurity decision-makers and calls on them to take Lean4's correctness seriously — all fixable, but formal verification of most software is far from trivial.
Related event: Lean4's Consistency Remains Unproven, Casting Doubt on Formal Verification(4 posts)→
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