Bourbaki

Remark

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

Integration, VI, p. 27, § 2. Vectorial measures . "

Suppose that there exists in Aq′A_q' a countable subset D that is dense for σ(F′,F)\sigma(F', F); then, the function q∘fq \circ f is always μ\mu-measurable, because q(f(t))=sup⁡z′∈D∣⟨z′,f(t)⟩∣q(f(t)) = \sup_{z' \in D} |\langle z', f(t) \rangle| (Ch. IV, §5, No. 4, Cor. 1 of Th. 2). Then, for every compact subset K of T, ∫K∗(q∘f) dμ=sup⁡J∫KgJ dμ\int_K^*(q \circ f)\, d\mu = \sup_J \int_K g_J\, d\mu, where J runs over the countable directed set of finite subsets of D (Ch. IV, §1, No. 1, Cor. of Th. 3); thus, one sees that in this case the condition that ∫K∗(q∘f) dμ<+∞\int_K^*(q \circ f)\, d\mu < +\infty for every compact subset K of T is necessary and sufficient for m to be qq-majorizable.

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

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Cites

Transcribed from the printed volume. Not translated.