Add <=> equivalence to expr parsing
Add <=> equivalence to expr parsing

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