Stepanets, O.I. (2001) “Approximation Characteristics of Spaces $S_\phi ^p$”, Ukrains’kyi Matematychnyi Zhurnal, 53(3), pp. 392–416. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4261 (Accessed: 10 April 2025).