Bourbaki

Corollary 1

Tag 01V0, permanent. Cite it as [Bourbaki, Tag 01V0].

Topologie algébrique, chapter II, § 5. Coégalisateur

Suppose that the group K is generated by the stabilisers of the vertices of G. Then the group homomorphism γo:Go→(G/K)γ(o)\gamma_o: G_o\rightarrow (G/K)_{\gamma(o)} is surjective. Moreover, if the groupoid G is simply transitive, the same is true of the groupoid G/KG/K.

The relation (R3′′R''_3) implies λ([e])=λ(ce)=γo(ce)\lambda ([e]) =\lambda (c_e) =\gamma_o(c_e). The relations (R3′′R''_3) then imply that the set of k∈Kk\in K such that λ([k])\lambda ([k]) belong to the image of γo\gamma_o is a subgroup of K. Finally, the relations (R3′R'_3) show that, for every element k∈Kk\in K whose stabiliser is not empty, λ([k])\lambda ([k]) belong to the image of γo\gamma_o. The corollary follows.

Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.

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Machine translation of the English, by gpt-5.4, against glossary version 34. Not checked by a person.