Shkapa, V. V. “Approximating Characteristics of the Classes $L_{β,p}^{ψ}$ of Periodic Functions in the Space $L_q$”. Ukrains’kyi Matematychnyi Zhurnal 67, no. 8 (August 25, 2015): 1139-1150. Accessed September 24, 2022. http://umj.imath.kiev.ua/index.php/umj/article/view/2052.