1. S. P. Burtsev, V. E. Zakharov, and A. V. Mikhailov, ?The method of the inverse problem with a variable spectral parameter,? Teor. Mat. Fiz.,70, No. 3, 323?341 (1987).
2. F. Kh. Mukminov and V. V. Sokolov, ?Integrable evolution equations with constraints,? Mat. Sb.,133, No. 3, 392?414 (1987).
3. N. Kh. Ibragimov and A. B. Shabat, ?On infinite-dimensional Lie-Bäcklund algebras,? Funkts. Anal. Prilozhen.,14, No. 4, 79?80 (1980).
4. S. I. Svinolupov and V. V. Sokolov, ?On evolution equations with nontrivial conservation laws,? Funkts. Anal. Prilozhen.,16, No. 4, 86?87 (1982).
5. V. V. Sokolov and A. B. Shabat, ?Classification of integrable evolution equations,? in: Soviet Scientific Reviews. Sec. C, Vol. 4, Harwood, New York (1984), pp. 221?280.