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 be coverings of B. Then the canonical morphisms oror and som som (I, p. 45, example 4) are isomorphisms.
For every point , it follows from the preceding proposition and from example 2 of I, p. 63, applied to the spaces , A, B and to the canonical injections, that the canonical morphism induces on passing to the stalks the identity of . It is therefore an isomorphism. The fact that 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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