sympy/sympy — pull request #1164 by mrocklin (2012-03-22 02:48:51+00:00)
Title: Clean sets - Union simplification

I went back over sets.py and simplified a number of things.

Notably Unions now work like Intersections.
Joining rules are distributed rather than collected in a mess in the union class.
This is substantially simpler than before and much easier to extend.

I also removed a lot of the empty interfaces like RealSet and CountableSet

The Real sets are gone (RealUnion, RealFiniteSet).