1. Birman, M.S., Solomyak, M.Z.: Piecewise polynomial approximations of functions of classes $W^{\alpha}_{p}$ . Mat. Sb. (N.S.) 73(115), 331–355 (1967)
2. Bordin, B., Kushpel, A., Levesley, J., Tozoni, S.: n-Widths of multiplier operators on two-point homogeneous spaces. In: Chui, C., Schumaker, L.L. (eds.) Approximation Theory IX, vol. 1, Theoretical Aspects, pp. 23–30. Vanderbilt University Press, Nashville (1998)
3. Bordin, B., Kushpel, A., Levesley, J., Tozoni, S.: Estimates of n-widths of Sobolev’s classes on compact globally symmetric spaces of rank 1. J. Funct. Anal. 202, 307–326 (2003)
4. Bourgain, J., Lindenstrauss, J., Milman, V.: Approximation of zonoids by zonotopes. Acta Math. 162, 73–141 (1989)
5. Carl, B.: Entropy numbers, s-numbers and eigenvalue problems. J. Funct. Anal. 41(3), 290–306 (1981)