Romanyuk, A. S., and S. Ya. Yanchenko. “Estimates of Approximation Characteristics and Properties of Operators of the Best Approximation for the Classes of Periodic Functions in the Space $B_{1,1}$”. Ukrains’kyi Matematychnyi Zhurnal 73, no. 8 (August 18, 2021): 1102 - 1119. Accessed May 2, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/6755.