1. N. I. Akhiezer and I. N. Glazman, Theory of Linear Operators in Hilbert Space, Ungar Press.
2. M. G. Krein and A. A. Nudel'man, The Markov Moment Problem and Extremal Problems [in Russian], Nauka, Moscow (1973).
3. I. S. Kats and M. G. Krein, ??-functions are analytic functions that map the upper half plane into itself,? Editor's Appendix in: F. Atkinson, Discrete and Continuous Boundary-Value Problems [Russian translation], Mir, Moscow (1968).
4. N. I. Akhiezer and M. G. Krein, On Certain Questions of Theory of Moments [in Russian], Gosudarstvennoe Ob"edinennoe Nauchno-Tekhnicheskoe Izd., Kharkov (1939).
5. S. T. Aleksandrov and V. V. Sobolev, ?The Loewner-Kurfarev equation for half plane and variation of univalent ?-functions,? in: Differential Equations and Their Applications [in Russian], Trudy Tyumen. Gos. Univ. (1980), pp. 8?30.