Bourbaki

Corollary

Tag 093L, permanent. Cite it as [Bourbaki, Tag 093L].

Integration, chapter V, § 5. Measures defined by numerical densities

— There exists a projector p of the space MC(T)\mathscr{M}_\mathbf{C}(T) onto the space Lloc1(T,μ;C)L^1_{\text{loc}}(T, \mu; \mathbf{C}), whose kernel p‾−1(0)\overline{p}^{-1}(0) is the set of complex measures alien to μ\mu, such that

∣θ∣=∣p(θ)∣+∣θ−p(θ)∣,p(∣θ∣)=∣p(θ)∣ |\theta| = |p(\theta)| + |\theta - p(\theta)|,\quad p(|\theta|) = |p(\theta)|

for every complex measure θ\theta.

If pp is restricted to the set of bounded measures, one obtains a projector p1p^1 of the space MC1(T)\mathscr{M}_\mathbf{C}^1(T) onto the space LC1(T,μ)L^1_\mathbf{C}(T, \mu); the relation ∥θ∥=∣θ∣(1)\| \theta \| = |\theta|(1) implies that ∥θ∥=∥p1(θ)∥+∥θ−p1(θ)∥\| \theta \| = \| p^1(\theta) \| + \| \theta - p^1(\theta) \| for every bounded complex measure θ\theta.

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

Cited by

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Cites

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Transcribed from the printed volume. Not translated.