Bourbaki

Corollary 2

Tag 0CC7, permanent. Cite it as [Bourbaki, Tag 0CC7].

General Topology, chapter X, § 2. Equicontinuous sets

Let XX be a compact space, YY a uniform space. Then every equicontinuous subset of F(X;Y)\mathscr{F}(X; Y) is uniformly equicontinuous.

Now suppose we have a set TT, a topological space XX, a uniform space YY and a mapping f:T×X→Yf : T \times X \to Y. Let f~\tilde{f} denote the mapping x→f(.,x)x \to f(., x) of XX into Fu(T;Y)\mathscr{F}_u(T; Y), and let us consider the canonical mapping θ:(t,g)→g(t)\theta : (t, g) \to g(t) of T×Fu(T;Y)T \times \mathscr{F}_u(T; Y) into YY. It is clear that the diagram

T×X→fY↓ιT×f~↑θT×Fu(T;Y) \begin{array}{ccc} T \times X & \xrightarrow{f} & Y \\ \downarrow_{\iota_T \times \tilde{f}} & & \uparrow \theta \\ T \times \mathscr{F}_u(T; Y) \end{array}

(where iTi_T is the identity mapping of T) is commutative. Suppose now that T is endowed with a topology and that, for each x∈Xx \in X, the mapping f(.,x):t→f(t.,x)f(., x) : t \to f(t., x) is continuous; we can then replace Fu(T;Y)\mathscr{F}_u(T; Y) by Cu(T;Y)\mathscr{C}_u(T; Y) in the above diagram. But we know that θ\theta is continuous from § 1, no. 6, Proposition 9; hence if f~\tilde{f} is continuous it follows that ff is continuous. Since the continuity of f~\tilde{f} can be expressed with the help of Proposition 1, we obtain the following result:

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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