1. Belkina, E.S., Platonov, S.S.: Equivalence of K-functionals and modulus of smoothness constructed by generalized dunkl translations. Izv. Vyssh. Uchebn. Zaved. Mat. 315(8), 3–15 (2008)
2. Bennett, C., Sharpley, R.: Interpolation of Operators Pure and Applied Mathematics, vol. 129. Academic Press, Orlando (1988)
3. Berens, H., Butzer, P.L., Pawelke, S.: Limitierungsverfahren von Reihen mehrdimensionaler Kugelfunktionen und deren Saturationsverhalten. Publ. RIMS Kyoto Univ. Ser. A. 4, 201–268 (1968)
4. Berens, H., Buter, P.L.: Semigroups of operators and approximation, vol. 145. Springer, Berlin (1967)
5. Bergh, J., Löfström, J.: Interpolation Spaces. An Introduction. Springer, Berlin (1976)