sympy/sympy — pull request #723 by smichr (2011-11-19 15:44:33+00:00)
Title: Product, Sum get is_zero and is_number methods and editing

Sum and Product are different than Integrals in that the order
of the limits doesn't change the sign of the result and the result
does not collapse if upper and lower limits are the same.

A number of Product problems (including trying to evaluate the unevaluated product) were remedied, too.