Bourbaki

Corollary 1 (Orthogonality relations)

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

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

Suppose G discrete and endowed with the counting measure. For xx and yy in G, one has

∫\int 0 if x≠yx\not=y

χ(x)χ(y)dχ= \chi (x)\chi (y)d\chi =

G^_{\widehat{G}} 1 if x=yx=y.

This results from the cor. to th. 1 of II, p. 215 and from duality.

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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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.