Lean Creator Leonardo de Moura: How a Claimed Proof Suspectedly Exploited Different Vulnerabilities to Bypass Two Independent Kernels
In the September 30, 2026 episode of Machine Learning Street Talk, Lean theorem prover creator Leonardo de Moura recounts how two independent checkers were deceived by different vulnerabilities in the Collatz proof incident, and discusses the architecture design of small trusted kernels and independent verifiers.
A piece of Lean code claiming to prove the Collatz conjecture passed verification from both the official Lean kernel and an independent checker, Nanoda—yet it appears each exploited a different vulnerability to do so. This is the account given by Leonardo de Moura, creator of the Lean theorem prover, on the September 30, 2026 episode of Machine Learning Street Talk. The episode was hosted by Tim Scarfe and lasted seventy-four minutes.
The program begins with why Lean deliberately maintains an extremely small trusted kernel, extending to the original intent and limitations of independent checkers. De Moura discussed introducing more checkers, the risks of reward hacking, achieving safety through transparency, and responded to governance questions regarding who controls the core of Lean.
De Moura founded Lean at Microsoft Research in 2013, initially with the goal of checking software code for correctness; he is also the co-creator of the SMT solver Z3. According to a book review in Science News, mathematicians and AI researchers have now become Lean's most active users. This episode also covers Lean's evolution from Lean 1 to Lean 4, how dependent types and Mathlib made formal proofs accessible to professional mathematicians, the role of AI agents in proof search ("breadcrumbs" rather than learning), and why certificates remain important in the era of AlphaProof and large language models.