Derev’yanko, N. V. “Approximation of the Classes $H_p^{Ω}$ of Periodic Functions of Many Variables in the Space $L_p$”. Ukrains’kyi Matematychnyi Zhurnal 66, no. 5 (May 25, 2014): 634–644. Accessed April 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2165.