1. B. S. Pavlov and L. D. Faddeev, "Null-sets operator functions with a positive imaginary part," J. Sov. Math.,26, No. 5 (1984).
2. B. S. Pavlov, "A uniqueness theorem for functions with a positive imaginary part," in: Problems in Mathematical Physics [in Russian], No. 4, Leningrad State Univ. (1970), pp. 118?124.
3. S. V. Petras, "Uniqueness theorem for operator R-functions," in: Problems in Mathematical Physics [in Russian], No. 7, Leningrad State Univ. (1974), pp. 126?135.
4. S. N. Naboko, "Uniqueness theorems for operator functions with positive imaginary part and singular spectrum in the self-adjoint Friedrichs model," Dokl. Akad. Nauk SSSR,275, No. 6, 1310?1313 (1984).
5. E. M. Stein, Singular Integrals and Differentiability Properties of Functions, Princeton Univ. Press (1970).