1. N. P. Korneichuk, Exact Constants in Approximation Theory (Nauka, Moscow, 1987).
2. V. M. Tikhomirov, Some Problems of the Approximation Theory (Mosk. Gos. Univ., Moscow, 1976).
3. K. I. Babenko, “Best approximations to a class of analytic functions,” Izv. Akad. Nauk
SSSR, Ser. Mat. 22, 631–640 (1958). https://www.mathnet.ru/eng/im3991.
4. V. M. Tikhomirov, “Approximation theory,” in Analysis 2: Progress in Science and Technology: Modern Problems of Mathematics. Fundamental Directions (VINITI, Moscow, 1987), Vol. 14, pp. 103–260.
5. L. V. Taikov, “On the best approximation in the mean of certain classes of analytic functions,” Math. Notes Acad. Sci. USSR 1, 104–109 (1967). https://doi.org/10.1007/BF01268058