Jane Street says formal methods are programming's future — and a team that banned JSON proved it with Lean 4 (blog.janestreet.com)
Jane Street argues the value of programming is shifting from writing code to verifying it: when GenAI produces tens of thousands of lines no one can review, formal specs and proofs become the affordable way to be certain. They point to OxCaml, seL4, Dafny and TLA+ as the industrial track.
A reverse engineer flagged the asterisk: seL4 is formally verified and still shipped gnarly bugs. The deeper crack came from a commenter who keeps trying for years: a formal spec is just 'the same implementation written a different way' and can carry the same bug.
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