ShabozovM. Sh., and Akobirshoev M. O. 2020. “Mean-Square Approximation by an Angle in $L_2$ and the Values of Quasiwidths for Some Classes of Functions”. Ukrains’kyi Matematychnyi Zhurnal 72 (6), 852-64. https://doi.org/10.37863/umzh.v72i6.1064.