Bourbaki

Remark

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

Integration, chapter V, § 1. Essential upper integral

— 1) If θ\theta is a complex measure on TT, one says that a function ff is θ\theta-moderated (resp. that θ\theta is moderated) if ff is ∣θ∣|\theta|-moderated (resp. if ∣θ∣|\theta| is moderated). 2) Every bounded measure is moderated; if TT is a countable union of compact sets, then every measure on TT is moderated. 3) Let (fn)(f_n) be a sequence of μ\mu-moderated functions with values in R‾\overline{\mathbf{R}}. For each nn, let UnU_n be an open set that is a countable union of open sets of finite outer measure, such that fnf_n is zero outside UnU_n. The function s=∑n∈N∣fn∣s = \sum_{n \in \mathbf{N}} |f_n| is then zero outside ⋃n∈NUn\bigcup_{n \in \mathbf{N}} U_n; it is therefore μ\mu-moderated, and the same is true of all functions ff such that ∣f∣≤s|f| \leq s. This applies in particular to the functions lim inf⁡n→∞fn\liminf_{n \to \infty} f_n, lim sup⁡n→∞fn\limsup_{n \to \infty} f_n and ∑n∈Nfn\sum_{n \in \mathbf{N}} f_n (if the sum is defined).

4) A function equal almost everywhere to a moderated function is moderated.

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

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Cites

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Transcribed from the printed volume. Not translated.