“Not a mere matter of programming”: an example
		• Proving programs correct has a 30+ year history – Given a specification (in a formal logic) and – an implementation (in a programming language), – prove that the implementation satisfies the specification • This has often been considered to be the key problem in software engineering
				{ true } x: int; read(x); if (mod(x,2) = 1) then    x := x + 1; fi { even(x) }