Simplify expression arguments
Simplify expression arguments

The previous release experimented with using a set data type to
automatically reduce expressions like a * b + a * b to just a * b.

There are two reasons to get rid of this by default:
1. It limits the ability to represent unsimplified expressions.
2. It adds some unnecessary computational overhead.

karissa/pyeda,karissa/pyeda,cjdrake/pyeda,GtTmy/pyeda,pombredanne/pyeda,karissa/pyeda,sschnug/pyeda,sschnug/pyeda,GtTmy/pyeda,cjdrake/pyeda,pombredanne/pyeda,cjdrake/pyeda,sschnug/pyeda,pombredanne/pyeda,GtTmy/pyeda