DoroninV. G., and LigunA. A. “Exact Constants in Jackson-Type Inequalities for $L_2$-Approximation on an Axis”. Ukrains’kyi Matematychnyi Zhurnal 61, no. 1 (January 25, 2009): 92-98. Accessed November 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3004.