@article{MZM_1981_29_2_a2,
     author = {V. I. Berdyshev},
     title = {Variation of the norms in the problem of best approximation},
     journal = {Matemati\v{c}eskie zametki},
     pages = {181--196},
     publisher = {mathdoc},
     volume = {29},
     number = {2},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1981_29_2_a2/}
}