NovikovO. A., and RukasovV. I. 1995. “Approximation of Classes of Continuous Functions by Generalized De La Vallée-Poussin Sums”. Ukrains’kyi Matematychnyi Zhurnal 47 (8), 1069–1079. https://umj.imath.kiev.ua/index.php/umj/article/view/5503.