Alphabeta Math
TheoremStatement: Literature-sourcedProof: AI-adaptedSession-authored (Fable 5 assisted)precheck passaudited 2026-08-11
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  • Literature-sourced — the exact statement appears in a cited source; only wording and notation differ.
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The conjugates of HH are in bijection with G/NG(H)G/N_G(H) and, for finite GG, number [G:NG(H)][G:N_G(H)]

Statement

Let HGH\le G. The rule

G/NG(H){gHg1:gG},gNG(H)gHg1,G/N_G(H)\longrightarrow\{gHg^{-1}:g\in G\},\qquad gN_G(H)\longmapsto gHg^{-1},

is a well-defined bijection. If GG is finite, the number of distinct conjugates of HH is [G:NG(H)][G:N_G(H)].

Facts & Assumptions

Given: A group GG and a subgroup HGH\le G.

[L3]

The normalizer is NG(H)={g:gHg1=H}N_G(H)=\{g:gHg^{-1}=H\} (The normalizer NG(H)={gG:gHg1=H}N_G(H)=\{g\in G:gHg^{-1}=H\} of a subgroup).

[L4]
[L5]

Conjugation by each gGg\in G is an automorphism of GG (Conjugation xgxg1x\mapsto gxg^{-1} is an automorphism).

Proof

technique · direct
1.1

Let GG act on the set of subgroups of GG by gK=gKg1g\cdot K=gKg^{-1}. By [L5], conjugation sends subgroups to subgroups, and the conjugation identities give the action laws.

L5
2.1

The orbit of HH is its set of conjugates, while [L3] says that its stabilizer is NG(H)N_G(H), a subgroup by [L4].

step 1.1L3L4
3.1

Applying [L1] gives the displayed bijection, and [L2] gives the finite count [G:NG(H)][G:N_G(H)].

step 2.1L1L2

Depends on

Used by

Dependency tree · next 3 levels

Direct dependencies and their dependencies through the next three levels: 43 results over 14 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.

Sources