cd /news/ai-safety/lean-4-bug-found-incidentally-by-ai-… · home topics ai-safety article
[ARTICLE · art-80107] src=twitter.com ↗ pub= topic=ai-safety verified=true sentiment=· neutral

Lean 4 Bug Found Incidentally by AI, "Proving" Collatz

An AI-generated formal proof in Lean claiming to solve the Collatz problem was found to exploit a bug in the Lean kernel, allowing any statement to be proven. The proof's author was aware of the soundness bug and used Collatz as a demonstration, not a serious solution.

read1 min views1 publishedJul 30, 2026
Lean 4 Bug Found Incidentally by AI, "Proving" Collatz
Image: source

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_tsenI 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.
── more in #ai-safety 4 stories · sorted by recency
── more on @lean 3 stories trending now
sponsored brought to you by zahid.host 4,200+ EU-deployed projects
reading about agents? ship yours in a single git push.

Run your AI side-project on zahid.host

EU-based hosting, git-push deploys, automatic HTTPS, no cold starts. Free tier with a custom domain — perfect for shipping the agent you just read about.

$git push zahid main
Live at https://your-agent.zahid.host
Get free account → Pricing
from €0/mo · no card required
LIVE [news/lean-4-bug-found-inc…] indexed:0 read:1min 2026-07-30 ·