Bourbaki

Remark 1

Tag 02K2, permanent. Cite it as [Bourbaki, Tag 02K2].

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

More generally, by the corollary to proposition 15 of II, p. 230, this formula is valid for every integrable complex function on Rn\mathbf{R}^n such that

∑x∈Λ∣f(x+y)∣<+∞ \sum_{x\in\Lambda}|f(x+y)|<+\infty

for every y∈Rny\in \mathbf{R}^n and such that the function on Tn\mathbf{T}^n defined by

y↦∑x∈Λf(x+y) y\mapsto \sum_{x\in\Lambda}f(x+y)

is continuous and admits an absolutely convergent Fourier series (cf. below).

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.