Babenko, V. F., and N. V. Parfinovych. “Nonsymmetric Approximations of Classes of Periodic Functions by Splines of Defect 2 and Jackson-Type Inequalities”.
Ukrains’kyi Matematychnyi Zhurnal 61, no. 11 (November 25, 2009): 1443–1454. Accessed April 11, 2025.
https://umj.imath.kiev.ua/index.php/umj/article/view/3113.