Bourbaki

Proposition 12

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

Integration, chapter VIII, § 4. Convolution of measures and functions

— Let pp and qq be two conjugate exponents (1≤p≤+∞1 \leq p \leq +\infty). If fχ−1/q∈L1(G,β)f \chi^{-1/q} \in L^1(G, \beta) and g∈Lp(G,β)g \in L^p(G, \beta), then ff and gg are convolvable, f∗gf * g is equal locally β\beta-almost everywhere to a function in Lp(G,β)L^p(G, \beta), and

∥f∗g∥p≤∥fχ−1/q∥1∥g∥p. \|f * g\|_p \leq \|f \chi^{-1/q}\|_1 \|g\|_p.
If f∈Lp(G,β)f \in L^p(G, \beta) and gχ′−1/q∈L1(G,β)g {\chi'}^{-1/q} \in L^1(G, \beta), then ff and gg are convolvable, f∗gf * g is equal locally β\beta-almost everywhere to a function in Lp(G,β)L^p(G, \beta), and
∥f∗g∥p≤∥f∥p∥gχ′−1/q∥1. \|f * g\|_p \leq \|f\|_p \|g {\chi'}^{-1/q}\|_1.
This follows from Props. 5 and 6 of No. 2 and the remarks in No. 4.

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

Cited by

Nothing.

Cites

Nothing.

Transcribed from the printed volume. Not translated.