1. V. M. Babich and V. S. Buldyrev, Asymptotic Methods in Short Wave Diffraction Problems (Nauka, Moscow, 1972) [in Russian].
2. H. Hönl, A. W. Maue, and K. Westpfahl, Theorie der Beugung (Springer, Berlin, 1961; Mir, Moscow, 1964).
3. Yu. A. Kravtsov and Yu. I. Orlov, Geometrical Optics of Inhomogeneous Media (Nauka, Moscow, 1980) [in Russian].
4. V. A. Borovikov and B. E. Kinber, Geometrical Theory of Diffraction (Svyaz’, Moscow, 1978) [in Russian].
5. P. L. Uslengni, Theory of the Scattering Waves (Academic, New York, 1978).