Romanyuk, A. S. “On Estimates of Approximation Characteristics of the Besov Classes of Periodic Functions of Many Variables”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 9 (September 25, 1997): 1250–1261. Accessed May 21, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5124.