V. P. Motornyi, “On Exact Estimates for the Pointwise Approximation of the Classes $W^rH^ω$ by Algebraic Polynomials”, Ukr. Mat. Zhurn., vol. 53, no. 6, pp. 783–799, Jun. 2001, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4299