Romanyuk, A. S. (1994). On Kolmogorov widths of classes $B^r_{p, \theta}$ of periodic functions of many variables with low smoothness in the space $L_q$. Ukrains’kyi Matematychnyi Zhurnal, 46(7), 915–926. https://umj.imath.kiev.ua/index.php/umj/article/view/5683