1. Abolinia, V.E., Myshkis, A.D.: Mixed problem for an almost linear hyperbolic system in the plane (in Russian). Mat. Sbornik 50(92)(4), 423–442 (1960)
2. Amerio, L., Prouse, G.: Almost-Periodic Functions and Functional Equations. The University Series in Higher Mathematics. Van Nostrand Reinhold Company, New York (1971)
3. Aronovich, G.V., Kartvelishvili, N.A., Lyubimtsev, Y.K.: Hydraulic Shock and Surge Tanks. Nauka, Moscow USSR (1968). (in Russian)
4. Bellman, R.E., Cooke, K.L.: Differential Difference Equations. Mathematics in Science and Engineering, vol. 6. Academic, New York (1963)
5. Boas, R.P.: Entire Functions. Pure and Applied Mathematics, vol. 5. Academic, New York (1954)