Formally verify code with Opus 5.5 + Lean: a few prompts yield 16 bug-fix PRs
julianweisser · x · 2026-09-23
Boris Cherny used Claude Opus 5.5 to formally verify the Claude Agent SDK with Lean — a couple of short prompts produced 16 PRs fixing bugs and race conditions. He also combines Lean with TLA+ to probe data flow, concurrency, and state management, noting Claude excels at both languages even though he doesn't. The resharing poster argues software verification is becoming a hot field with lots of tooling still to build.
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