@article{SM_1990_67_1_a6,
     author = {I. G. Tsar'kov},
     title = {The inequality of {Jackson} type for abstract functions},
     journal = {Sbornik. Mathematics},
     pages = {117--142},
     year = {1990},
     volume = {67},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1990_67_1_a6/}
}