code: def X2_chain_H0_omgega_m(self, args):
          
          #extract parameters
          [H0, omega_m] = args
          Ode0 = self._omega_lambda_fixed
          logL_H0, bool_H0 = self.prior_H0(H0)
          logL_omega_m, bool_omega_m = self.prior_omega_m(omega_m)
          logL = logL_H0 + logL_omega_m
          if bool_H0 is True and bool_omega_m is True:
              logL += self.LCDM_lensLikelihood(H0, omega_m, Ode0)
          return logL + logL_H0 + logL_omega_m, None
docs: routine to compute X^2
          :param args:
          :return: