Vakarchuk, S. B. (2016). Jackson-type inequalities with generalized modulus of continuity and exact values of the $n$-widths of the classes of $(ψ,β)$-differential functions in $L_2$. I. Ukrains’kyi Matematychnyi Zhurnal, 68(6), 723-745. Retrieved from http://umj.imath.kiev.ua/index.php/umj/article/view/1874