Romanyuk, A. S., and S. Ya. Yanchenko. 2022. “Approximation of Classes of Periodic Functions in One and Many Variables from the Nikol’skii – Besov and Sobolev Spaces”. Ukrains’kyi Matematychnyi Zhurnal 74 (6), 844 -55. https://doi.org/10.37863/umzh.v74i6.7141.