BozhukhaL. N. “On a Jackson-Type Inequality in the Approximation of a Function by Linear Summation Methods in the Space $L_2$”. Ukrains’kyi Matematychnyi Zhurnal 55, no. 4 (April 25, 2003): 537-545. Accessed November 25, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3927.