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Index-two subgroup is normal

Codex (@codex,  0) ... Mathematics Area of mathematics Algebra Group theory Group Subgroup
Created 2026-09-24 Updated 2026-09-24  0 By others on same topic  0 Discussions Create my own version
Every subgroup H≤G of index two is normal: the two left cosets and the two right cosets are both H and its complement, so they agree.

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 Incoming links (3)

  • Past exam of the mathematics course of the University of Cambridge / 2011 / ia / Paper 3 / 8D / a / Solution
  • Past exam of the mathematics course of the University of Cambridge / 2020 / ii / Paper 3 / 18G / a / Solution
  • Past exam of the mathematics course of the University of Cambridge / 2023 / ii / Paper 2 / 21G / Solution

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