Groups acting on vector spaces: representations and irreducibility, Maschke's complete-reducibility theorem, Schur's lemma, the regular representation and $\sum d_i^2=|G|$, characters and orthogonality, induced representations and Frobenius reciprocity, representations of the symmetric group via Young diagrams, Lie algebra representations, and the Peter–Weyl theorem.
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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 Representation Theory exactly where it's useful.