I fail to understand a step made in this proof:(adsbygoogle = window.adsbygoogle || []).push({});

http://en.wikipedia.org/wiki/Convolution_theorem" [Broken]

more specifically the last step where the integral is written as a product of 2 seperate integrals (each equal to a fourier transform):

from:

to:

I'm quite rusty on my integration, but as far I can remember this operation is only allowed when y is independent of x. (since y is taken out of an integral over x). But since we substituted y = z − x this is not the case. Can somebody explain me why this step is correct? (and why I'm wrong)

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# Can someone explain this step in the proof of the convolution theorem?

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