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PropositionStatement: AI-adaptedProof: AI-adaptedPipeline-generatedprecheck passjudge pass (gpt-5.6-terra)audited 2026-09-14
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Translations are diffeomorphisms and their differentials trivialize the tangent bundle

Statement

Assume ACω. For every g in a Lie group G, the maps Lg and Rg are diffeomorphisms with respective inverses Lg−1 and Rg−1. Moreover,

ΦL:G×TeG⟶TG,ΦL(g,X)=d(Lg)eX,

and

ΦR:G×TeG⟶TG,ΦR(g,X)=d(Rg)eX,

are smooth vector-bundle isomorphisms over id⁡G.

The countable-choice assumption is used exactly through the supplied theorem that equips tangent bundles and global differentials with their smooth structures.

Facts & Assumptions

Given: ACω, a Lie group G with identity e, and g∈G.

[F1]

ACω is countable choice. The Axiom of Countable Choice (ACω).

[F2]

Left and right translations are Lg(h)=gh and Rg(h)=hg, and both are smooth. Left and right translations on a Lie group.

[F3]

Assuming ACω, the global differential of a smooth map is smooth between the canonical smooth tangent bundles. Assuming countable choice, the global differential of a smooth map is smooth.

[F4]

The differential of a diffeomorphism is a linear isomorphism on every tangent space. The differential of a diffeomorphism is an isomorphism.

[F5]

A fibrewise bijective smooth bundle map over a diffeomorphism is a vector-bundle isomorphism. A fibrewise bijective smooth bundle map over a diffeomorphism is a bundle isomorphism.

Proof

technique · direct
1.1F2algebra

The group laws give Lg∘Lg−1=Lg−1∘Lg=id⁡G and Rg∘Rg−1=Rg−1∘Rg=id⁡G. All four translations are smooth by [F2], so Lg and Rg are diffeomorphisms with the asserted inverses.

1.2F1F2F3algebra

Let m:G×G→G be multiplication. Near an arbitrary g0, choose product coordinates in which m is represented by a smooth map μ(a,b). The local matrix of d(Lg)e is the second-variable Jacobian D2μ(a,be), whose entries are smooth in a. Equivalently, this is the restriction of the smooth global differential dm supplied by [F3]. Therefore ΦL is a smooth bundle map. The same calculation with the variables reversed gives smoothness of ΦR.

2.1F4step 1.1

By [F4] and step 1.1, each fibre map d(Lg)e:TeG→TgG and d(Rg)e:TeG→TgG is a linear isomorphism. Hence ΦL and ΦR are fibrewise linear bijections over id⁡G.

3.1F5step 1.1step 2.1step 1.2

Apply [F5] to the smooth fibrewise bijections from steps 2.1 and 1.2 over id⁡G. Both ΦL and ΦR are vector-bundle isomorphisms. Fibrewise, their inverses are (g,V)↦(g,d(Lg−1)gV) and (g,V)↦(g,d(Rg−1)gV), respectively.

4.1F1F2F3F4F5step 1.1step 2.1step 1.2step 3.1∎

A Lie group is nonempty. If dim⁡G=0, all tangent fibres are zero spaces and the displayed maps are the unique fibre maps; if dim⁡G=1, the same proof applies. No metric or nondegeneracy condition occurs, and the group is boundaryless by the page convention. The only choice assumption is the stated ACω, used through [F3] for the canonical smooth tangent bundles/global differential; all group operations and local computations are supplied or pointwise and add no choice. The item asserts explicit inverse identities but no biconditional.

Depends on

Dependency tree · 2 levels

Sources