sympy/sympy — pull request #2158 by Tempel (2013-06-07 16:23:05+00:00)
Title: Test and fix for Point.is_collinear coincident point error.

Previously, if the first two points passed to Point.is_collinear were
coincident, the method would always return True. This is fixed by converting
the point list to a set to remove identical points.