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TheoremStatement: Literature-sourcedProof: AI-adaptedPipeline-generatedprecheck passjudge pass (gpt-5.6-terra)audited 2026-09-14
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Stabilizers are closed embedded Lie subgroups

Statement

Assume ACω. For a smooth action of a Lie group G on a Hausdorff smooth manifold M, every stabilizer Gx is a closed embedded Lie subgroup of G.

Facts & Assumptions

Given: ACω, a smooth left action of G on a Hausdorff smooth manifold M, and x∈M.

[A1]

The stabilizer is a subgroup and the orbit map Φx(g)=g⋅x is smooth. Orbits, stabilizers, and orbit maps of smooth actions.

[A2]

A closed subgroup has its unique embedded Lie-subgroup structure under countable choice. The Axiom of Countable Choice (ACω), Cartan closed subgroup theorem.

[F1]

The manifold convention is Hausdorff, so singletons are closed. Topological manifolds without boundary: Hausdorff, second-countable, and locally Euclidean spaces.

Proof

technique · realize the stabilizer as a closed fibre
1.1A1F1

By [F1], {x} is closed in M. Since Φx is continuous by [A1], Gx=Φx−1({x}) is closed in G. It is a subgroup by the action laws in [A1].

2.1A2step 1.1∎

Apply [A2] to the closed subgroup from step 1.1. It receives its unique embedded Lie-subgroup structure. If the action is trivial then Gx=G; if it is free then Gx={e}. No properness, transitivity, connectedness, or effectiveness is used. Countable choice is used only through [A2].

Depends on

Dependency tree · 2 levels

Sources