HrabovaU. Z., and SerdyukA. S. “Order Estimates for the Best Approximations and Approximations by Fourier Sums of the Classes of (ψ, β)-Differential Functions”. Ukrains’kyi Matematychnyi Zhurnal 65, no. 9 (September 25, 2013): 1186–1197. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2500.