Romanyuk, A. S. (1997) “On estimates of approximation characteristics of the Besov classes of periodic functions of many variables”, Ukrains’kyi Matematychnyi Zhurnal, 49(9), pp. 1250–1261. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5124 (Accessed: 17May2024).