# Lean 4 Bug Found Incidentally by AI, "Proving" Collatz > Source: > Published: 2026-07-30 11:29:39+00:00 So, someone came up with an AI-generated formal proof, in Lean, of a solution to the Collatz problem, and it turned out that the “proof” was merely exploiting a bug in the Lean kernel (allowing you to prove anything). - * Not that this changes any of the above, but I am informed that the person posting the proof was actually aware that this was a Lean kernel soundness bug, and it was not intended to be taken seriously as a solution to Collatz's problem.Replying to [@gro_tsen](https://x.com/gro_tsen)I think they just use collatz as a fun way to demonstrate the lean soundness bug. There is a history of this in the theorem proving community. The author knew it was a soundness bug and it was intentional. - I think they just use collatz as a fun way to demonstrate the lean soundness bug. There is a history of this in the theorem proving community. The author knew it was a soundness bug and it was intentional. # Join the conversation