V. F. Babenko and N. V. Parfinovych, “Nonsymmetric approximations of classes of periodic functions by splines of defect 2 and Jackson-type inequalities”, Ukr. Mat. Zhurn., vol. 61, no. 11, pp. 1443–1454, Nov. 2009, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3113