Bourbaki

Proposition 12

Tag 08T3, permanent. Cite it as [Bourbaki, Tag 08T3].

Integration, chapter IV, § 4. Integrable functions and sets

— For a measure μ\mu on a locally compact space XX to be bounded (Ch. III, §1, No. 8), it is necessary and sufficient that XX be an integrable set with respect to μ\mu (or, what comes to the same thing, that every finite constant function be integrable); in this case,

∥μ∥=∣μ∣(X)=∫d∣μ∣. \| \mu \| = | \mu |(X) = \int d|\mu|.

For, we have seen that ∣μ∣∗(X)=∥μ∥|\mu|^*(X) = \| \mu \| (§ 1, No. 2); the proposition therefore follows from Prop. 10 of No. 6.

For every bounded measure μ\mu, we again say that μ(X)\mu(X) is the total mass of μ\mu.

It follows from Th. 4 of No. 6 that if μ\mu is a bounded measure then, for every ε>0\varepsilon > 0, there exists a compact set KK such that ∣μ∣(CK)≤ε|\mu|(CK) \leq \varepsilon.

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.