1. C. Gardner, J. Greene, M. Kruskal, and R. Miura, Phys. Rev. Lett.,19, 1095 (1967).
2. V. E. Zakharov and L. D. Faddeev, Funktsional. Analiz i Ego Prilozhen.,5, 18 (1971).
3. L. A. Takhtadzhyan and L. D. Faddeev, Teor. Mat. Fiz.,21, 160 (1974).
4. V. E. Zakharov and A. B. Shabat, Funktsional. Analiz i Ego Prilozhen.,8, 43 (1974).
5. L. D. Faddeev, “Inverse problem of the quantum theory of scattering. II.” in: Modern Problems of Mathematics [in Russian], Itogi Nauki i Tekhniki, VINITI,3 (1974), p. 93.