def _unpack_truisms(self, c):
try:<EOL><INDENT>op = getattr(self, '<STR_LIT>'+c.op)<EOL><DEDENT>except AttributeError:<EOL><INDENT>return set()<EOL><DEDENT>return op(c)<EOL>
Given a constraint, _unpack_truisms() returns a set of constraints that must be True
this constraint to be True.