Bourbaki

Proposition 9

Tag 021H, permanent. Cite it as [Bourbaki, Tag 021H].

Topologie algébrique, chapter IV, § 2. Groupes de Poincaré des espaces délaçables

Let X be an unravelable topological space and let W\mathscr{W} be a basis for the topology of X. For every point xx of X, the cardinal of the group π1(X,x)\pi_1(X, x) is bounded above by sup(Card(W\mathscr{W}), Card(N\mathbf{N})). In particular, the Poincaré group of a metric space of countable type and unravelable is countable.

In fact, the space λx(X)\lambda_x(X) endowed with the endpoint mapping is a connected covering of X whose fibre at xx is π1(X,x)\pi_1(X, x). The assertion then results from I, p. 40, th. 3.

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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Cites

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