V. N. . Konovalov, “Approximation of functions from the Sobolev space by algebraic polynomials”, Ukr. Mat. Zhurn., vol. 44, no. 5, pp. 613–617, May 1992, Accessed: Feb. 17, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/7956