VakarchukS. B., and ZabutnayaV. I. “On the Best Polynomial Approximation in the Space L2 and Widths of Some Classes of Functions”. Ukrains’kyi Matematychnyi Zhurnal 64, no. 8 (August 25, 2012): 1025-1032. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2637.