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2. J. Galejs, Terrestrial Propagation of Long and Very Long Waves, Pergamon, New York (1977).
3. G. I. Makarov and V. V. Novikov, in: Problems in Wave Diffraction and Propagation [in Russian], 3rd ed., LGU, Leningrad (1968), p. 19.
4. Ya. A. Al'pert, É. G. Guseva, and D. S. Fligel', Propagation of Low-Frequency Waves in the Earth-Ionosphere Waveguide [in Russian], Fizmatgiz, Moscow (1967).
5. A. B. Orlov and G. V. Azarnin, Problems in Wave Diffraction and Propagation [in Russian], 10th ed., LGU, Leningrad (1970), p. 39.