Bourbaki

Proposition 11

Tag 08N8, permanent. Cite it as [Bourbaki, Tag 08N8].

Integration, chapter III, § 2. Support of a measure

— Every measure with compact support is bounded.

For, ∣μ∣|\mu| is also a measure with compact support, thus we can restrict attention to the case that μ≥0\mu \geq 0; if hh is a continuous mapping of XX into [0,1][0, 1], with compact support and equal to 1 on Supp(μ)\mathrm{Supp}(\mu), then for every function f∈K(X;C)f \in \mathscr{K}(X; \mathbf{C}) one has ∣f(x)∣≤∥f∥h(x)|f(x)| \leq \|f\| h(x) on Supp(μ)\mathrm{Supp}(\mu), therefore (Cor. 2 of Prop. 8) μ(∣f∣)≤μ(h)∥f∥\mu(|f|) \leq \mu(h)\|f\|, which proves the proposition (§ 1, No. 8).

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.