@article{MZM_1999_66_4_a1,
     author = {S. B. Vakarchuk},
     title = {$K$-functionals and exact values of $n$-widths of some classes in~$L_2$},
     journal = {Matemati\v{c}eskie zametki},
     pages = {494--499},
     publisher = {mathdoc},
     volume = {66},
     number = {4},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1999_66_4_a1/}
}