Romanyuk, A. S., and V. S. Romanyuk. 2019. “Estimates of Some Approximating Characteristics of the Classes of Periodic Functions of One and Many Variables”. Ukrains’kyi Matematychnyi Zhurnal 71 (8): 1102-15. https://umj.imath.kiev.ua/index.php/umj/article/view/1501.