1. I. M. Gel’fand, “Certain Questions of Analysis and Differential Equations,” Usp. Mat. Nauk 14(3), 3–19 (1959).
2. G. M. Struchina, “Conjugation Problem for Two Equations,” Inzh.-Fiz. Zhurn. 4(11), 99–104 (1961).
3. Ya. S. Uflyand, “Propagation of Oscillations in Composite Electric Lines,” Inzh.-Fiz. Zhurn. 7(1), 89–92 (1964).
4. L. A. Zolina, “The Boundary-Value Problem for a Model Hyperbolic-Parabolic Equation,” Zhurn. Vychisl. Matem. i Matem. Fiz. 6(6), 991–1001 (1966).
5. A. M. Nakhushev and Kh. G. Bzhikhatlov, “One Boundary-Value Problem for a Mixed-Type Equation,” Sov. Phys. Dokl. 183(2), 261–264 (1968).