Rukasov, V. I., and E. S. Silin. “Approximation of Continuous Functions of Low Smoothness by De La Vallee-Poussin Operators”. Ukrains’kyi Matematychnyi Zhurnal 57, no. 3 (March 25, 2005): 394–399. Accessed May 3, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3607.