Does anybody know how to prove the following?(adsbygoogle = window.adsbygoogle || []).push({});

[tex]\sum\limits_{n=0}^{\infty} \sum\limits_{m=0}^{\infty} f(n,m) = \sum\limits_{p=0}^{\infty} \sum\limits_{q=0}^{p} f(p,p-q)[/tex]

f(n,m) is any function of n and m.

Note the change of the limiting values on the sums.

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# Double series

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