1. V. E. Zakharov, S. V. Manakov, S. P. Novikov, and L. P. Pitaevskii, Theory of Solitons: The Inverse Scattering Technique [in Russian], Nauka, Moscow (1980).
2. M. J. Ablowitz, Stud. Appl. Math.,58, 17 (1978).
3. L. D. Faddeev, in: Solitons. Topics in Current Physics (ed. B. K. Bullough), Vol. 17, Springer (1980), pp. 339?354.
4. P. P. Kulish and A. G. Reiman, in: Problems of Quantum Field Theory and Statistical Physics [in Russian], Zap. Nauchn. Seminarov Leningr. Otd. Mat. In-Ta Akad. Nauk SSSR,77, 134 (1978).
5. D. Mumford and P. Moerbecke, Acta Mathem.,143, 93 (1979); J. Moser, Adv. Math.,16, 197 (1975).