get the names of the prior information eqs that
        are listed as greater than inequality constraints.  Zero-
        weighted pi are skipped

        Returns
        -------
        pandas.Series : pilbl of prior information that are non-zero weighted
                        greater than constraints

def greater_than_pi_constraints(self):
        """get the names of the prior information eqs that
        are listed as greater than inequality constraints.  Zero-
        weighted pi are skipped

        Returns
        -------
        pandas.Series : pilbl of prior information that are non-zero weighted
                        greater than constraints

        """

        pi = self.prior_information
        gt_pi = pi.loc[pi.apply(lambda x: self._is_greater_const(x.obgnme) \
                                          and x.weight != 0.0, axis=1), "pilbl"]
        return gt_pi