sympy/sympy — pull request #2245 by jrioux (2013-07-03 11:29:26+00:00)
Title: Fix nested sum evaluation.

Fix the evaluation of nested sums that contain a KroneckerDelta. Also fix the evaluation of sums that contain a Piecewise, which is the return value of deltasummation in most cases.

Fixes issue 3924: Evaluation of nested sums.
http://code.google.com/p/sympy/issues/detail?id=3924