1. L. V. Ovsyannikov, “Lagrange approximations in the theory of waves [in Russian],” in: Nonlinear Problems in the Theory of Surface and Internal Waves, Nauka, Novosibirsk (1985), pp. 10–77.
2. L. Debnath, Nonlinear Water Waves, Acad. Press, Boston, Mass. (1983).
3. N. I. Makarenko, “The second long-wave approximation in the Cauchy-Poisson problem [in Russian],” in: Dynamics of a Continuous Medium, No. 77, Inst. Hydrodynamics, Russ. Acad. Sci., Novosibirsk (1986), pp. 56–72; W. Craig, Comm. Partial Differential Equations, 10, 787–1003 (1985); T. Kano and T. Nishida, Osaka J. Math., 23, 389–413 (1986); L. V. Ovsyannikov, “On foundations of the theory of shallow water [in Russian],” in: Dynamics of a Continuous Medium, No. 15, Inst. Hydrodynamics, Russ. Acad. Sci., Novosibirsk (1973), pp. 104–125.
4. V. I. Karpman and E. M. Maslov, Soviet Phys. JETP, 46, 537–559 (1977); E. M. Maslov, Theor. Math. Phys., 42, 237–245 (1980); V. P. Maslov and G. A. Omel’yanov, Russ. Math. Surveys, 36, No. 3, 73–149 (1981); Siberian Math. J., 24, 787–795 (1983); A. C. Newell, “The inverse scattering transform,” in: Solitons (Topics Current Phys., Vol. 17, R. K. Bullough and P. J. Caudrey, eds.), Springer, Berlin (1980), pp. 177–242; L. A. Kalyakin, Theor. Math. Phys., 92, 736 (1992).
5. V. A. Baikov and S. A. Kordyukova, Quaest. Math., 26, 1–14 (2003); S. A. Kordyukova, Nonlinear Dynam., 46, 73–85 (2006).