AI agents just machine-checked the longest proof in mathematics 🧮

Some proofs are so long that checking every step by hand is almost impossible. The Classification of Finite Simple Groups is the most famous example: roughly 15,000 pages, spread over more than 500 articles by about 100 mathematicians, nicknamed "the enormous theorem". On 26 October, Axiom Math released what it calls the first complete computer-checked proof of it, written in the Lean proof assistant. For me, this is one of the most beautiful agent stories of the year.

What was actually done

Finite simple groups are the "atoms" of symmetry. The classification says every one of them is either a cyclic group of prime order, an alternating group, one of sixteen infinite families of groups of Lie type, or one of exactly 26 sporadic groups, the largest being the Monster with about 8 × 10^53 elements.

Axiom rewrote the first-generation proof in Lean, a language precise enough that a computer checks every single logical step. The public repository is "sorry-free", which means no step was skipped or left as an assumption, and it uses only Lean's standard axioms. The final statement is short: every finite simple group is isomorphic to a group on the classification list.

How the agents worked

This is the part that fascinates me as someone who builds agent systems. The project started on 1 October with a Slack channel and a proof map assembled from the literature, split into 108 milestones and about 380 smaller tasks. Over 24 days, engineers and mathematicians directed swarms of dozens of AI agents that produced about 43.1 million lines of Lean.

Agents claimed tasks through GitHub issues, delegated missing prerequisites to other agents, and pushed results into a shared repository. Lead agents broke down hard arguments and reviewed statements. Engineers built a shared build cache because agents were writing proofs faster than Lean could recheck them. And when early milestones turned out to rest on unproven assumptions, the team deleted tens of thousands of lines and replanned. That honesty about what failed is exactly what makes the result convincing.

What the machines found

Formalization does not let you wave your hands. The agents surfaced 34 noteworthy deviations from the published record. Most were small, like typos, table errors or dropped hypotheses. One was substantial: in John Walter's 1986 route to the Unbalanced Group Theorem, the agents found explicit counterexamples to a closure assertion. Working with group theorists Richard Lyons and Ronald Solomon, AxiomProver produced and formalized an alternative argument, including a new result Axiom calls "Preservation of simple tops", written up in an accompanying paper.

The honest part

Axiom is careful here, and I appreciate it. Humans still have to check that the formal statement really says what we mean; Lean checks the deductions. The formalization also follows a different route than Walter at one point, so it is not a step-by-step replay of the history. The errata list is still being compiled with an advisory board of group theorists. The theorem itself remains the achievement of the mathematicians who built it.

Why it matters

Results across algebra, number theory and even physics lean on this classification, often in one sentence. Now that dependency is explicit and checkable. And for agent builders, it shows a pattern worth copying: many agents, a shared dependency map, and a strict machine checker that refuses to accept "looks right".

Sources

Decades of human insight, now checked line by line. That feels like a good use of AI.

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