Lean Formalization Confirms Gap in Mochizuki’s ABC Conjecture Proof

A recent Lean formalization effort has identified a gap in Mochizuki’s claimed proof of the ABC conjecture. The verification was highlighted in a tweet by Fumiharu Kato, referencing the Lean result. The gap concerns a specific step in the intricate inter‑universal Teichmüller theory. Experts note that the issue does not automatically invalidate the entire proof. The discovery underscores the challenges of formally checking highly complex mathematics. It also demonstrates the growing role of proof assistants in scrutinizing major results. The mathematical community is awaiting further clarification from Mochizuki’s team. The incident may prompt additional formal verification efforts on the proof.