Bourbaki

Definition 1

Tag 08NN, permanent. Cite it as [Bourbaki, Tag 08NN].

Integration, III, p. 33, § 3. Integrals of continuous vector-valued functions

For every function f∈K~(X;E)f \in \widetilde{\mathscr{K}}(X;E) we call integral of ff with respect to μ\mu, and denote by ∫fdμ\int f d\mu or ∫f(x)dμ(x)\int f(x) d\mu(x), or ∫fμ\int f \mu, or ∫f(x)μ(x)\int f(x)\mu(x), the element of E′∗{E'}^* defined by

⟨∫fdμ,z′⟩=∫⟨f,z′⟩dμfor all z′∈E′. \left\langle \int f d\mu, z' \right\rangle = \int \langle f, z' \rangle d\mu \quad \text{for all } z' \in E'.

We note that even if EE is Hausdorff and f∈K(X;E)f \in \mathscr{K}(X;E), one does not necessarily have ∫fdμ∈E\int f d\mu \in E (Exer. 1; cf. No. 3).

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

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Transcribed from the printed volume. Not translated.