# Where can I find rigorous statements about the spectral decomposition of reductive groups?

Given a global field $F$ and a reductive group $G$, where can I find the spectral decomposition of $$L^2( Z(\mathbb{A}) G(F) \backslash G( \mathbb{A})).$$

I will need the result in this generality, means for a general reductive group and for function and number fields.

I have just seen some instances of such theorems yet and would be happy about a reference. Of course, I expect that the function field and number field case have been treated, but probably in different places.

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