debugger22/sympy — pull request #7 by debugger22 (2014-05-19 11:19:17+00:00)
Title: modify simultaneous subs to avoid dummy variables

While subs is smart enough not to put a Number into a dummy
variable of something like Derivative, xreplace is not so
simultaneous subs (which uses xreplace) is modified to use
a product of dummies to so subs will ignore the Derivative-like dummy
variables.