1. F. I. Frankl’, “Subsonic flow about a profile with a supersonic zone,” Prikl. Mat. Mekh. 20(2), 196–202 (1956).
2. A. V. Bitsadze and A. A. Samarskii, “On some simple generalizations of linear elliptic boundary problems,” Dokl. Akad. Nauk SSSR 185, 739–740 (1969) [Soviet Math. Dokl. 10, 398–400 (1969)].
3. K. B. Sabitov, “Tricomi problem for a mixed parabolic-hyperbolic equation in a rectangular domain,” Mat. Zametki 86(2), 273–279 (2009) [Math. Notes 86 (2), 249–254 (2009)].
4. N. I. Ionkin, “The solution of a certain boundary-value problem of the theory of heat conduction with a nonclassical boundary condition,” Differ. Uravn. 13(2), 294–304 (1977).