sympy/sympy — pull request #1928 by amitjamadagni (2013-03-24 17:33:57+00:00)
Title: Issue #3581:Implement arg.rewrite(atan2)

I hope this was what to be implemented.Hope this is right and there is a multi value function for different values of x and y but can this be symbolically implemented.
http://en.wikipedia.org/wiki/Inverse_trigonometric_functions