1. Frankl’, F.I., Subsonic Flow About a Profile with a Supersonic Zone, Prikl. Mat. Mekh., 1956, vol. 20, no. 2, pp. 196–202.
2. Devingtal’, Yu.V., The Existence and Uniqueness of the Solution of a Problem of F.I. Frankl’, Izv. Vyssh. Uchebn. Zaved. Mat., 1958, no. 2 (3), pp. 39–51.
3. Lin Jianbing, Some Frankl’s Problems, Vestnik Leningrad. Gos. Univ. Mat. Mekh. Astron., 1961, no. 3 (13), pp. 28–39.
4. Salakhitdinov, M.S. and Mirsaburov, M., Nelokal’nye zadachi dlya uravnenii smeshannogo tipa s singulyarnymi koeffitsientami (Nonlocal Problems for Mixed-Type Equations with Singular Coefficients), Tashkent, 2005.
5. Polosin, A.A., On the Unique Solvability of the Tricomi Problem for a Special Domain, Differ. Uravn., 1996, vol. 32, no. 3, pp. 394–401.