Fedunyk, O. V. “Linear Widths of the Classes $B^{\Omega}_{p, \theta}$ of Periodic Functions of Many Variables in the Space $L_q$”. Ukrains’kyi Matematychnyi Zhurnal 58, no. 1 (January 25, 2006): 93–104. Accessed May 3, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3435.