1. I. M. Gelfand, ‘‘Some a questions of analysis and differential equations,’’ Am. Math. Soc. Transl., II Ser. 26, 201–219 (1963).
2. Y. S. Uflyand, ‘‘Propagation of oscillations in composite electric lines,’’ Inzh.-Fiz. Zh. 7, 89–92 (1964).
3. L. A. Zoline, ‘‘On a boundary-value problems for a model equation of hyperbolic-parabolic type,’’ Zh. Vychisl. Mat. Mat. Fiz. 6, 991–1001 (1966).
4. O. A. Ladizhenskaya and L. Stupyalis, ‘‘On mixed type equations,’’ Vestn. Leningr. Uinv., Ser. Mat.-Mekh.-Astron. 19 (4), 38–46 (1965).
5. T. D. Dzhuraev, Boundary-Value Problems for Equation of Mixed and Mixed Composite Types (Fan, Tashkent, 1979) [in Russian].