@article{MZM_1973_14_6_a16,
     author = {V. Yu. Popov},
     title = {Best mean-square approximation of functions of $m$ variables},
     journal = {Matemati\v{c}eskie zametki},
     pages = {913--924},
     publisher = {mathdoc},
     volume = {14},
     number = {6},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1973_14_6_a16/}
}