@article{DAN_1975_223_6_a5,
     author = {V. A. Morozov and A. I. Grebennikov},
     title = {On optimal approximation of operators},
     journal = {Doklady Akademii Nauk},
     pages = {1307--1310},
     publisher = {mathdoc},
     volume = {223},
     number = {6},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1975_223_6_a5/}
}