Derev’yanko, N. V. 2014. “Approximation of the Classes $H_p^{Ω}$ of Periodic Functions of Many Variables in the Space $L_p$”. Ukrains’kyi Matematychnyi Zhurnal 66 (5): 634–644. https://umj.imath.kiev.ua/index.php/umj/article/view/2165.