1. D. V. Gorbachev, “Jackson's theorem in $$\mathfrak{L}_P (S^{N - 1} )$$ ,” in:Abstracts of Papers of the Voronezh Winter School “Contemporary Methods of Function Theory and Related Problems of Mathematics and Mechanics” [in Russian], Izd. Voronezh Gos. Univ., Voronezh (1997), p. 56.
2. N. Ya. Vilenkin,Special Functions and Group Representation Theory [in Russian], Nauka, Moscow (1991).
3. Handbook of Mathematical Functions With Formulas, Graphs, and Mathematical Tables, (M. Abramowitz and I. Stegun, editors), National Bureau of Standards, Washington, D.C. (1964).
4. A. G. Babenko, “Sharp Jackson-Stechkin inequality inL 2 for multidimensional spheres”Mat. Zametki [Math. Notes],60, No. 3, 333–355 (1996).
5. N. P. Korneichuk,Extremum Problems in Approximation Theory [in Russian], Nauka, Moscow (1976).