'Use Mace4 to build a first order model.
:return: ``True`` if a model was found (i.e. Mace returns value of 0),
else ``False``'

def _build_model(self, goal=None, assumptions=None, verbose=False):

    if (not assumptions):
        assumptions = []
    (stdout, returncode) = self._call_mace4(self.prover9_input(goal, assumptions), verbose=verbose)
    return ((returncode == 0), stdout)
