@article{IVM_1981_12_a9,
     author = {V. Yu. Popov},
     title = {Exact constants in {Jackson} inequalities for best spherical mean square approximations},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {67--78},
     year = {1981},
     number = {12},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1981_12_a9/}
}