1. V. M. Tikhomirov, “Approximation theory,” in Analysis – 2, Itogi Nauki i Tekhniki. Ser. Sovrem. Probl. Mat. Fund. Napr. (VINITI, Moscow, 1987), Vol. 14, pp. 103–260.
2. A. Pinkus, $$n$$-Widths in Approximation Theory (Springer- Verlag, Berlin, 1985).
3. S. D. Fisher, Function Theory on Planar Domains. A Second Course in Complex Analyses (John Wiley & Sons, New York, 2007).
4. Yu. A. Farkov, “On the best linear approximation of holomorphic functions,” J. Math. Sci. 218 (5), 678–698 (2016).
5. S. B. Vakarchuk and M. Sh. Shabozov, “The widths of classes of analytic functions in a disc,” Sb. Math. 201 (8), 1091–1110 (2010).