Romanyuk, A. S. “On Estimates of the Kolmogorov Widths of the Classes $B_{p,θ}^r$ in the Space $L_q$”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 53, no. 7, July 2001, pp. 996-1001, https://umj.imath.kiev.ua/index.php/umj/article/view/4320.