1. C.S. Gardner, J.M. Greene, M.D. Kruskal, R.M Miura: Phys. Rev. Lett. 19, 1095 (1967);
2. C.S. Gardner, J.M. Greene, M.D. Kruskal, R.M Miura: Commun. Pure Appl. Math. 27, 97 (1974)
3. M. Wadati, M. Toda: J. Phys. Soc. Jpn. 32, 1403 (1972)
4. P.D. Lax: Commun. Pure Appl. Math. 21, 467 (1968)
5. V.E. Zakharov, A.B. Shabat: Soviet Phys. JETP 34, 62 (1972)