RukasovV. I., & ChaichenkoS. O. (2002). Approximation of the Classes $C^{{\bar \psi }} H_{\omega }$ by de la Vallée-Poussin Sums. Ukrains’kyi Matematychnyi Zhurnal, 54(5), 681-691. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4107