1. G.B. Whitham, Linear and Nonlinear Waves, Wiley, New York, 1974.
2. V.M. Babich, V.S. Buldyrev, Asymptotic Method in Short-waves Diffraction Theory, Springer, Berlin, 1991.
3. Asymptotic solutions of the second order equation system concentrated in a neighborhood of the ray;Nomofilov;Zapiski Nauch. Semin. LOMI AN SSSR,1980
4. Complex space–time ray method and quasiphotons;Babich;Zapiski. Nauch. Semin. LOMI AN SSSR,1981
5. V.M. Babich, V.S. Buldyrev, I.A. Molotkov, Space–Time Ray Method, Linear and Nonlinear Waves, Leningrad University Press, Leningrad, 1985 (in Russian).