Hrabova, U. Z., & Serdyuk, A. S. (2013). Order Estimates for the Best Approximations and Approximations by Fourier Sums of the Classes of (ψ, β)-Differential Functions. Ukrains’kyi Matematychnyi Zhurnal, 65(9), 1186–1197. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/2500