Shabozov, M. Sh., and M. O. Akobirshoev. “Mean-Square Approximation by an Angle in $L_2$ and the Values of Quasiwidths for Some Classes of Functions”. Ukrains’kyi Matematychnyi Zhurnal 72, no. 6 (June 17, 2020): 852-864. Accessed April 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1064.