StepanetsO. I. “Approximation Characteristics of Spaces $S_\phi ^p$”. Ukrains’kyi Matematychnyi Zhurnal 53, no. 3 (March 25, 2001): 392-416. Accessed November 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4261.