When the Proof Checker Can't Check Itself
An AI-assisted "disproof" of the Collatz conjecture turned out to be an adversarial proof object threading through two independent bugs in Lean's type kernel and its external verifier. The hole was patched in an hour, but the Lean creator's warning lands harder than the bug itself: AIs are getting good at finding and exploiting soundness issues in proof checkers, and that's not a one-time event.
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