def _g_1(self):
        """omega1 < omega < omega2"""
        # return 3 * self._n_1() / (self._omega - self._vertices_omegas[0])
        return (3 * self._f(1, 0) * self._f(2, 0) /
                (self._vertices_omegas[3] - self._vertices_omegas[0]))