formally verified? In high-school maths, we are introduced to the idea of a proof — the word “proof” is etymologically related to the word “probe”. In a proof, we reason from first principles (aka axioms), why a certain assertion (aka theorem) holds true. Said differently, we verify the theorem, and proof represents the verification process. The axioms and the proof need a language in which they are represented — at a minimum, this language involves a syntax and a set of proof rules governing that syntax. This mathematical rule-based verification is also called formal verification, to distinguish it from the colloquial use of the word verification which may just involve human inspection.