1. L. I. Slepyan, Nonstationary Elastic Waves (Sudostroenie, Leningrad, 1972) [in Russian].
2. L. I. Slepyan, Mechanics of Cracks (Sudostroenie, Leningrad, 1990) [in Russian].
3. D. I. Trubetskov and A. G. Rozhnev, Linear Oscillations. and Waves (Fizmatlit, Moscow, 2001) [in Russian].
4. B. M. Levitan and V. V. Zhikov, Almost-Periodic Functions. and Differential Equations (Mosk. Gos. Univ., Moscow, 1978) [in Russian].
5. A. Zygmund, Trigonometric Series (Cambridge Univ. Press, Cambridge, 1959; Mir, Moscow, 1965).