Proofs treated as mathematical objects with a shape, a size and an ordinal. Covers the sequent calculus and cut elimination as an algorithm, Herbrand's theorem, constructive interpretations, ordinal analysis from Gentzen to the modern programme, and the complexity of proofs themselves.
Free to start · adaptive placement finds your level · reviews timed to your own forgetting.
Every idea is taught with motivation and a worked example before the drills, and an FSRS spaced-repetition engine schedules each review for the day its model predicts you would forget it. A short placement check finds what you already know, so you start Proof Theory exactly where it's useful.