Height, width and Dilworth, product against lexicographic order, complete lattices and the Knaster-Tarski fixed-point theorem, closure operators and Galois connections, formal concept analysis, the distributive and modular hierarchies with their two forbidden diagrams, Birkhoff representation, Heyting algebras and Stone duality, Scott continuity and the fixed-point semantics of recursion, and the Dedekind-MacNeille completion.
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 Order Theory exactly where it's useful.