1. P. B. Burt:Phys. Lett. A,109, 133 (1985).
2. A. Actor:Rev. Mod. Phys.,51, 469 (1979).
3. P. B. Burt:Quantum, Mechanics and Nonlinear Waves (Harhood, N. Y., 1981).
4. H. T. Davis:Introduction to Nonlinear Differential and Integral Equations (Dover, New York, N. Y., 1962).
5. G. Baker jr. andP. Graves-Morris:Pade Approximations, Part II (Addison-Wesley, Reading Mass., 1981).