1. S. M. Nikol’skii, Quadrature Formulas (Nauka, Moscow, 1988) [in Russian].
2. S. M. Nikol’skii, “On estimates for approximation by quadrature formulas,” Usp. Mat. Nauk 5 (2), 165–177 (1950).
3. A. N. Kolmogorov, “Über die beste Annäherung von Funktionen einer gegebenen Functionenklasse,” Ann. Math., Ser. 2, 37, 107–110 (1936). See also: “On the best approximation of functions of a given function class,” in Selected Works. Mathematics and Mechanics (Nauka, Moscow, 1985), pp. 186–189 [in Russian].
4. S. A. Smolyak, “On optimal recovery of functions and functionals on them,” Cand. Sci. (Phys.–Math.) Dissertation (Mosk. Gos. Univ., Moscow, 1965).
5. K. Yu. Osipenko, “Optimal interpolation of analytic functions,” Mat. Zametki 12 (4), 465–476 (1972) [Math. Notes 12, 712–719 (1972)].