PichugovS. A. “Multiple Modules of Continuity and the Best Approximations of Periodic functions in Metric Spaces”. Ukrains’kyi Matematychnyi Zhurnal 70, no. 5 (May 25, 2018): 699-707. Accessed November 21, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1588.