code: def _g(self, x, tau):
          
          return tau ** 2 * (tau ** 2 + 1) ** -2 * (
                  (tau ** 2 + 1 + 2 * (x ** 2 - 1)) * self.F(x) + tau * np.pi + (tau ** 2 - 1) * np.log(tau) +
                  np.sqrt(tau ** 2 + x ** 2) * (-np.pi + self.L(x, tau) * (tau ** 2 - 1) * tau ** -1))
docs: analytic solution of integral for NFW profile to compute deflection angel and gamma
  
          :param x: R/Rs
          :type x: float >0