Vakarchuk, S. B. (2004). Jackson-type inequalities and exact values of widths of classes of functions in the spaces $S^p , 1 ≤ p < ∞$. Ukrains’kyi Matematychnyi Zhurnal, 56(5), 595–605. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/3780