1. M. Toda, Theory of Nonlinear Lattices (Springer-Verlag, Heidelberg, 1981; Mir, Moscow, 1983).
2. M. Kac and P. van Moerbeke, Proc Nat. Ocad. Sci. 72, 1627–1629 (1975).
3. Yu. M. Berezanskii, Dokl. Akad. Nauk SSSR 281, 16–19 (1985).
4. N. V. Zhernakov, Ukr. Mat. Zh. 39, 645–648 (1987).
5. G. Teschl, Jacobi Operators and Completely Integrable Nonlinear Lattices (Am. Math. Soc., Providence, RI, 2000).