formal-verification
4 free lessons tagged formal-verification across Computer Science. Each one is a short sequence of focused steps with narration and a five-question quiz at the end — take them in any order, no signup required.
What Has Actually Been Verified, and What It Cost
Two landmark systems carry machine-checked proofs of real code: a C compiler and an operating system kernel. Their published effort figures give the honest price of full verification, and their trusted computing bases show exactly what a proof still leaves unproved. This lesson uses both to decide where verification pays.
Model Checking: Exhaustive Search Instead of Proof
The third tradition supplies no invariants and writes no proofs. It builds the set of states a system can reach and checks the property against all of them, which is decidable when that set is finite. This lesson covers what it buys, the state explosion that limits it, and the techniques that made it usable anyway.
Types as Propositions: Making Wrong Programs Unwritable
The other tradition does not prove a program correct after writing it. It designs a type that only correct programs inhabit, so the compiler's ordinary check is the proof. This lesson builds the correspondence between types and logic, shows what dependent types add, and covers the price the approach charges.
What a Proof of Correctness Actually Is
Testing samples inputs; a proof covers all of them. The machinery is a logic in which programs are statements about how they change what is true. This lesson builds Hoare triples, works a proof by hand, and identifies the one step that cannot be automated and is therefore where the work is.