Bourbaki

Corollary 1

Tag 01Q3, permanent. Cite it as [Bourbaki, Tag 01Q3].

Topologie algébrique, chapter I, § 4. Revêtements

Let B be a topological space and A a subspace of B. Suppose that the spaces A and B are locally connected. Let E and E′E' be coverings of B. Then the canonical morphisms ψ:M\psi :\mathscr{M}orB(E;E′)A→M_B(E; E')_A\rightarrow \mathscr{M}orA(EA;EA′)_A(E_A; E'_A) and ψ′:I\psi ':\mathscr{I}somB(E;E′)A→_B(E; E')_A\rightarrow I\mathscr{I}somA(EA;EA′)_A(E_A; E'_A) (I, p. 45, example 4) are isomorphisms.

For every point a∈Aa\in A, it follows from the preceding proposition and from example 2 of I, p. 63, applied to the spaces {a}\{a\}, A, B and to the canonical injections, that the canonical morphism ψ\psi induces on passing to the stalks the identity of EaEa′E^{E'_a}_a. It is therefore an isomorphism. The fact that ψ′\psi ' is an isomorphism is proved analogously.

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.