A. S. Serdyuk and I. V. Sokolenko, “Linear approximation methods and the best approximations of the Poisson integrals of functions from the classes $H_{ω_p}$ in the metrics of the spaces $L_p$”, Ukr. Mat. Zhurn., vol. 62, no. 7, pp. 979–996, Jul. 2010, Accessed: Apr. 23, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2930