Myronyuk, V. V. “Kolmogorov Widths of the Anisotropic Besov Classes of Periodic Functions of Many Variables”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 68, no. 5, May 2016, pp. 634-43, https://umj.imath.kiev.ua/index.php/umj/article/view/1867.