convergence are performed in the computation of LT. Usually
      the solution is found after three iterations. The relative
      error present in this case is at most

          (V/C)**4
         ----------
          1 - (V/C)

      which is well approximated by (V/C)**4.

         The precision of this computation (ignoring round-off
         error) is better than 4e-11 seconds for any pair of objects
         less than 50 AU apart, and having speed relative to the
         solar system barycenter less 