1. Zakharov, V.E., Manakov, S.V., Novikov, S.P., Pitaevski, L.P.: Theory of solitons. Method of the inverse problem. Moscow: Nauka 1980
2. Solitons. Topics in Current Physics, Vol. 17, Bullough R, Caudrey, P. (eds.). Berlin, Heidelberg, New York: Springer 1980
3. Ablowitz, M.J., Segur, H.: Solitons and inverse scattering transform. Philadelphia: SIAM 1981
4. Gardner, C.S., Green, J.H., Kruskal, H.D., Miura, R.M.: Commun. Pure Appl. Math.27, 97 (1974)
5. Olver, P.J.: Evolution equations possessing infinitely many symmetries. J. Math. Phys.18, 1212?1215 (1977)