— There exists a projector p of the space MC(T) onto the space Lloc1(T,μ;C), whose kernel p−1(0) is the set of complex measures alien to μ, such that
∣θ∣=∣p(θ)∣+∣θ−p(θ)∣,p(∣θ∣)=∣p(θ)∣
for every complex measure θ.
If p is restricted to the set of bounded measures, one obtains a projector p1 of the space MC1(T) onto the space LC1(T,μ); the relation ∥θ∥=∣θ∣(1) implies that ∥θ∥=∥p1(θ)∥+∥θ−p1(θ)∥ for every bounded complex measure θ.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.