omega2 < omega < omega3

def _g_2(self):
        """omega2 < omega < omega3"""
        return 3 / (self._vertices_omegas[3] - self._vertices_omegas[0]) * (
            self._f(1, 2) * self._f(2, 0) +
            self._f(2, 1) * self._f(1, 3))