%0 Journal Article %A S. B. Vakarchuk %T Best Polynomial Approximations and Widths of Classes of Functions in the Space~$L_2$ %J Matematičeskie zametki %D 2018 %P 307-311 %V 103 %N 2 %I mathdoc %U http://geodesic.mathdoc.fr/item/MZM_2018_103_2_a12/ %G ru %F MZM_2018_103_2_a12