Definition
Plain language
A piece of software with a machine-checked mathematical proof that it does what it should on every input.
As stated in the literature
A program paired with a formal proof, checked by a proof assistant like Rocq, Lean, or Coq, establishing that the implementation satisfies its specification across all inputs, message orderings, and failure scenarios.
Also called: verified systems
Why it matters: In safety-critical settings, a proof is qualitatively stronger evidence than any amount of testing, because it covers inputs no test could ever try.
For example, a verified file system comes with a proof that it never loses data even under crashes or concurrent writes.
Heard on the show
“… with why a year is even the baseline, because the gap between "I wrote some code" and "I have a verified system" is enormous, and most listeners have never sat on the verified side of it. …”Episode 075 — Growing Code and Proof Together: Verified Systems in Ten Hours Instead of a Year