1. V. E. Zakharov et al., The Theory of Solitons. The Inverse Scattering Method [in Russian], Nauka, Moscow (1980).
2. B. A. Dubrovin, V. B. Matveev, and S. P. Novikov, Usp. Mat. Nauk,31, 55 (1976).
3. J. Moser, Lecture Notes in Phys.,38, 467 (1975).
4. M. A. Olshanetsky and A. M. Perelomov, Phys. Rep.,71, 313 (1981).
5. E. K. Sklyanin, Funktsional. i Analiz Prilozhen.,21, 86 (1987).