SolichK. V. “Kolmogorov Widths of the Classes $B^{\Omega}_{p, \theta}$ of Periodic Functions of Many Variables in the Space $L_q$”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, no. 10, Oct. 2012, pp. 1416-25, https://umj.imath.kiev.ua/index.php/umj/article/view/2668.