1. L. A. Takhtadzhyan and L. D. Faddeev,The Hamiltonian Methods in the Theory of Solitons [in Russian], Nauka, Moscow (1986); English transl.: L. D. Faddeev and L. A. Takhtajan, Berlin, Springer (1987).
2. V. E. Zakharov, S. V. Manakov, S. P. Novikov, and L. P. Pitaevskii,Theory of Solitons: The Inverse Scattering Method [in Russian], Nauka, Moscow (1980); English transl.: S. P. Novikov, S. V. Manakov, L. P. Pitaevsky, and V. E. Zakharov, Plenum, New York (1984).
3. A. V. Zabrodin,JETP Letters,66, 620–625 (1997).
4. E. K. Sklyanin,J. Sov. Math.,19, 1546–1596 (1982).
5. A. G. Izergin and V. E. Korepin,Lett. Math. Phys.,5, 199–205 (1981);Nucl. Phys. B,205, 401–413 (1982).