Popov, P.A. (2001) “An Analog of the Jackson Inequality for Coconvex Approximation of Periodic Functions”, Ukrains’kyi Matematychnyi Zhurnal, 53(7), pp. 919–928. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4313 (Accessed: 7 April 2025).