Vakarchuk SB. Generalized characteristics of smoothness and some extremе problems of the approximation theory of functions in the space $L_2 (R)$. I. Ukr. Mat. Zhurn. [Internet]. 2018 Sep. 25 [cited 2025 Dec. 5];70(9):1166-91. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/1627