Bourbaki

Exercise 14, § 2

Integration, VI, p. 65

a) Let GG be a Banach space, F=G′F = G' its strong dual, gg a mapping of TT into FF belonging to the space ΛGp\Lambda_G^p (§1, Exer. 16). Show that if p>1p > 1, the measure g⋅μg \cdot \mu is absolutely continuous with respect to μ\mu (for the strong topology of FF).

b) Take for GG the Banach space L1(N)L^1(\mathbf{N}), so that G′=L∞(N)G' = L^\infty(\mathbf{N}); if ff is the function defined in Exer. 7*a*) of §1 (regarded as taking its values in G′G'), then ff is scalarly well integrable but the measure f⋅μf \cdot \mu is not absolutely continuous with respect to μ\mu for the strong topology of G′G'.

Solution

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Transcribed from the printed volume. Not translated.