Babenko, V. F., and S. V. Konareva. “Jackson – Stechkin-Type Inequalities for the Approximation of Elements of Hilbert Spaces”. Ukrains’kyi Matematychnyi Zhurnal 70, no. 9 (September 25, 2018): 1155-1165. Accessed June 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1626.