N. V. Parfinovych, “Exact values of the best (α, β) -approximations of classes of convolutions with kernels that do not increase the number of sign changes”, Ukr. Mat. Zhurn., vol. 69, no. 8, pp. 1073–1083, Aug. 2017, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/1759