RomanyukA. S., & YanchenkoS. Y. (2021). Estimates of approximation characteristics and properties of operators of the best approximation for the classes of periodic functions in the space $B_{1,1}$. Ukrains’kyi Matematychnyi Zhurnal, 73(8), 1102 - 1119. https://doi.org/10.37863/umzh.v73i8.6755