Bourbaki

Lemma 7

Tag 02J1, permanent. Cite it as [Bourbaki, Tag 02J1].

Théories spectrales, chapter II, § 1. Transformation de Fourier

Let (Gi)i∈I(G_i)_{i\in I} and (Hi)i∈I(H_i)_{i\in I} be finite families of locally compact topological groups. For i∈Ii\in I, let θi:Gi×Hi→U\theta_i: G_i\times H_i\rightarrow \mathbf{U} be a mapping which puts the groups GiG_i and HiH_i in duality. The mapping θ\theta defined by

θ((gi),(hi))=∏i∈Iθi(gi,hi) \theta ((g_i),(h_i)) =\prod_{i\in I}\theta_i(g_i, h_i)

puts the groups ∏Gi\prod G_i and ∏Hi\prod H_i in duality.

This results from Proposition 2 of II, p. 206 and from the preceding definition.

Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.

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Cites

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Machine translation of the English, by gpt-5.4, gpt-5-6-mini, against glossary version 34. Not checked by a person. That model is a cut down version of the one the rest of this language was written by.