1. I. I. Privalov, Boundary Properties of Analytic Functions (Gosudarstv. Izdat. Tehn. -Teor. Lit., Moscow–Leningrad, 1950) [in Russian].
2. G. Ts. Tumarkin and S. Ya. Khavinson, “Classes of analytic functions in multiply connected domains,” in Research on Modern Problems of the Theory of Functions of a Complex Variable (Fizmatgiz, Moscow, 1960), pp. 45–77 [in Russian].
3. G. S. Litvinchuk and I. M. Spitkovskii, Factorization of Measurable Matrix Functions, in Operator Theory: Advances and Applications (Birkhäuser Verlag, Basel, 1987), Vol. 25.
4. F. D. Gakhov, “The Riemann boundary-value problem for a system of n pairs of functions,” Uspekhi Mat. Nauk 7 (4 (50)), 3–54 (1952).
5. I. M. Spitkovskii, “Factorization of measurable matrix functions. Related questions of the theory of systems of singular integral equations and the vector Riemann boundary value problem. I,” Differ. Uravn. 17 (4), 697–709 (1981).