1. J. J. Stoker, Water Waves. Mathematical Theory and Applications, Interscience, New York (1957).
2. J. Witham, Linear and Nonlinear Waves, Wiley, New York (1974).
3. L. V. Ovsyannikov, N. I. Makarenko, and V. I. Nalimov, Nonlinear Problems of the Theory of Surface and Internal Waves [in Russian], Nauka, Novosibirsk (1985).
4. V. Yu. Liapidevskii and V. M. Teshukov, Mathematical models of long wave propagation in an inhomogeneous fluid [in Russian], Izd. Sib. Otd. Ross. Akad. Nauk, Novosibirsk (2000).
5. V. M. Teshukov, “Hyperbolicity of the Long-Wave Equations,” Dokl. Akad. Nauk SSSR, 284, No. 3, 555–562 (1985).