Bourbaki

Proposition 10

Tag 09NM, permanent. Cite it as [Bourbaki, Tag 09NM].

Integration, chapter IX, § 1. Premeasures and measures on a topological space

— If g is a μ\mu-measurable mapping with values in a topological space G (Hausdorff or not), there exists a μ\mu-crushing (Lβ)β∈B(L_\beta)_{\beta \in B} of T such that the restrictions gLβg_{L_\beta} are continuous for all β∈B\beta \in B.

Consider a crushing (Kα)α∈A(K_\alpha)_{\alpha \in A} of T for μ\mu. Since the mapping gg is measurable, there exists for each α∈A\alpha \in A a partition of KαK_\alpha into a sequence (Kαn)(K_{\alpha n}) of compact sets and a locally negligible set NαN_\alpha, such that the restriction of gg to each of the sets KαnK_{\alpha n} is continuous. The family (Kαn)(α,n)∈A×N(K_{\alpha n})_{(\alpha, n) \in A \times \mathbf{N}} is then the sought-for crushing. For, it is locally countable, and the set N′=N∪(⋃αNα)N' = N \cup (\bigcup_\alpha N_\alpha) is locally negligible, because a compact set intersects at most a countable infinity of sets NαN_\alpha.

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

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Cites

Nothing.

Transcribed from the printed volume. Not translated.