Bourbaki

Theorem 2

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

Topologie algébrique, chapter I, § 2. Applications étales

Let B be a topological space and A a subspace of B. Make one of the following hypotheses:

(i) A admits a fundamental system of paracompact neighbourhoods;

(ii) B is paracompact and A closed;

(iii) B is metrizable;

(iv) A is compact and two distinct points of A possess disjoint neighbourhoods in B.

Then every continuous section over A of an étale mapping p:E→Bp: E\rightarrow B extends to a continuous section of pp over a neighbourhood of A.

Consider the following property (PCV) of the pair (B,A)(B,A):

(PCV) For every covering (Ui)i∈I(U_i)_{i\in I} of A by open subsets

of B, there exists a neighbourhood V of A and a locally

finite family (Fj)j∈J(F_j)_{j\in J} of closed subsets of V covering V, such that

each of the FjF_j is contained in one of the UiU_i.

Theorem 2 follows from Lemmas 1 and 3 below.

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.

Cited by

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Cites

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