1. E. K. Sklyanin, ?On complete integrability of the Landau-Lifshitz equation,? Preprint LOMI E-3-1979 [in English], Leningrad Branch, V. A. Steklov Mathematics Institute, USSR Academy of Sciences, Leningrad (1979).
2. C. N. Yang, ?S-matrix for the one-dimensional n-body problem with repulsive or attractive ?-function interaction,? Phys. Rev.,168, 1920 (1968).
3. V. E. Zakharov and A. V. Mikhailov, ?Relativistically invariant two-dimensional field theory models which can be integrated by the inverse scattering technique,? Zh. Eksp. Teor. Fiz.,74, 1953 (1978).
4. R. J. Baxter, ?Partition function of the eight-vertex lattice model,? Ann. Phys. (N. Y.),70, 193 (1972).
5. E. K. Sklyanin, L. A. Takhtadzhyan, and L. D. Faddeev, ?Quantum inverse scattering method. I,? Preprint LOMI R-I-79 [in Russian], Leningrad Branch, V. A. Steklov Mathematics Institute, USSSR Academy of Sciences, Leningrad (1979).