Bourbaki

Proposition 5

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

Integration, chapter VI, § 2. Vectorial measures . "

— Let q be a lower semi-continuous semi-norm on F. Let m be a q-majorizable measure, and let f be a function essentially integrable for m and such that ∫fdm∈F\int f dm \in F. Then

q(∫fdm)≤∫∙∣f∣dq(m). q\left( \int f dm \right) \leq \int^\bullet |f| dq(m).

For,

q(∫fdm)=sup⁡z′∈Aq′∣⟨z′,∫fdm⟩∣≤sup⁡z′∈Aq′∫∣f∣d∣z′∘m∣≤∫∙∣f∣dq(m) q\left( \int f dm \right) = \sup_{z' \in A'_q} \left| \langle z', \int f dm \rangle \right| \leq \sup_{z' \in A'_q} \int |f| d|z' \circ m| \leq \int^\bullet |f| dq(m)

by virtue of (1) and the relation ∣z′∘m∣≤q(m)|z' \circ m| \leq q(m) for z′∈Aq′z' \in A'_q.

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.