1. V. L. Ginzburg, The Propagation of Electromagnetic Waves in Plasmas, Pergamon Press, Oxford, New York (1970).
2. L. M. Brekhovskikh, Waves in Layered Media [in Russian], Nauka, Moscow (1973).
3. V. M. Babich and V. S. Buldyrev, Asymptotic Methods in the Short-Wave Diffraction Problems [in Russian], Nauka, Moscow (1972).
4. V.P. Maslov, The Complex WKB Method in Nonlinear Equations [in Russian], Nauka, Moscow (1977).
5. L. Ostrovsky, Asymptotic Perturbation Theory of Waves, Imperial College Press, London (2015).