J. Prestin, V. V. Savchuk, and A. L. Shydlich, “Direct and inverse theorems on the approximation of 2π -periodic functions by Taylor – Abel – Poisson operators”, Ukr. Mat. Zhurn., vol. 69, no. 5, p. 657, May 2017, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/1725