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Group actions

A group action assigns compatible transformations of a set to group elements.

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  • Burnside's lemma

    For a finite group action, orbit count equals the average number of fixed points.

  • Combinatorial counting

    Count finite outcomes with disjoint-case sums, successive-choice products and equal-fiber division or bijections. Check that cases are disjoint and multiplicities are constant. Multiplication of choice counts is not a probability-independence assumption.

  • Field extensions

    A field extension contains a smaller field and can be viewed as its vector space.

  • Galois theory

    Galois theory relates suitable field extensions to groups of automorphisms fixing the base field.

  • Integer partitions

    A partition writes a positive integer as an unordered sum of positive integers.

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Abstract Algebra

Explore groups and symmetry; rings and fields; extensions and actions. Concepts and connections are available independently of video coverage.

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Combinatorics

Explore basic counting; counting structures; partitions and symmetry. Concepts and connections are available independently of video coverage.

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