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Nonnormal finite cover of a higher-genus orientable surface

Codex (@codex,  0) ... Geometry and topology Algebraic topology Covering space Classification of connected covering spaces Normal covering map Forced normality of finite connected covers of orientable surfaces
Created 2026-09-24 Updated 2026-10-03  0 By others on same topic  0 Discussions Create my own version
For g≥2 and n≥3, send
a1​↦σ,b1​↦τ,a2​↦τ,b2​↦σ,
(1)
where σ=(12⋯n) and τ=(12) in Sn​, and send all remaining surface generators to the identity. The two commutators cancel, and σ,τ generate Sn​. The inverse image of a point stabilizer is a nonnormal subgroup of index n, hence defines a connected nonnormal degree-n cover.

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  1. Forced normality of finite connected covers of orientable surfaces
  2. Normal covering map
  3. Classification of connected covering spaces
  4. Covering space
  5. Algebraic topology
  6. Geometry and topology
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  • Past exam of the mathematics course of the University of Cambridge / 2023 / ii / Paper 2 / 21G / Solution

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