30% of Git modelled in Lean 4 with coding agents, 8,000+ theorems proven, 100+ potential bugs found
kfountou · x · 2026-10-24
In a two-month experiment, Natalie Marleny formalized roughly 30% of Git in Lean 4, leaning heavily on coding agents, and proved over 8,000 theorems about the implementation.
The effort uncovered more than 100 potential defects in Git v2.55, at least two of which may be security vulnerabilities. The team also built a differential random testing (DRT) harness with the largest corpus of pinned differential test cases for Git implementations — 10k+ unique tests — and used them against their own small TypeScript Git implementation, with plans to differentially test all major Git implementations next.
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