One invariant built twice: complete a monoid of projective modules into a group, and a ring's arithmetic, a manifold's topology and a field's Galois theory all turn out to be recorded in the same place. Covers K_0 through K_2, Whitehead torsion, Quillen's higher theory and the finite-field computation.
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 Algebraic K-Theory exactly where it's useful.