Bourbaki

Corollary 3

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

Integration, VIII, p. 17, § 2. Linear representations of groups

*Let GG be a locally compact group, EE a quasi-complete locally convex space, and UU a continuous linear representation of GG in EE. Let β\beta be a positive measure on GG, aa an element of GG, and B\mathscr{B} a base for the filter of neighborhoods of aa, formed of compact neighborhoods. For every V∈BV \in \mathscr{B}, let fVf_V be a continuous function ⩾0\geqslant 0 on GG, with support contained in VV, and such that ∫fV dβ=1\int f_V\, d\beta = 1. Then, for every x∈Ex \in E,

U(a)x=lim⁡VU(fV⋅β)x, U(a)x = \lim_V U(f_V \cdot \beta)x,

the limit being taken with respect to the section filter of B\mathscr{B}.

The mapping s↦U(s)xs \mapsto U(s)x of GG into EE is continuous. By Cor. 2, U(a)x=lim⁡V∫(U(s)x)⋅fV(s) dβ(s)U(a)x = \lim_V \int (U(s)x) \cdot f_V(s)\, d\beta(s) with respect to the section filter of B\mathscr{B}, that is, U(a)x=lim⁡VU(fV⋅β)xU(a)x = \lim_V U(f_V \cdot \beta)x.

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

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Transcribed from the printed volume. Not translated.