Rukasov, V. I. “Approximation of Continuous Functions by De La Vallée-Poussin Operators”.
Ukrains’kyi Matematychnyi Zhurnal
55, no. 3 (March 25, 2003): 414–424. Accessed April 27, 2025.
https://umj.imath.kiev.ua/index.php/umj/article/view/3915
.