What survives when you stop naming the operations: signatures and algebras, subuniverses and generation, congruences and the congruence lattice, subdirect products and Birkhoff's representation theorem, terms and free algebras, the HSP theorem, equational logic and its completeness, clones and polynomial operations, Mal'cev conditions, Jónsson terms and congruence distributivity, congruence modularity, the lattice of subvarieties, quasivarieties, polymorphisms and the constraint satisfaction dichotomy, the finite basis problem, and the commutator.
Free to start · adaptive placement finds your level · reviews timed so it stays learned.
Every idea is taught with motivation and a worked example before the drills, and an FSRS spaced-repetition engine schedules each review for the moment just before you'd forget it. A short placement check finds what you already know, so you start Universal Algebra exactly where it's useful.