@article{DAN_1979_248_4_a2,
     author = {M. Otelbaev},
     title = {Estimates for the approximation numbers of operators connected with elliptic equations},
     journal = {Doklady Akademii Nauk},
     pages = {783--787},
     year = {1979},
     volume = {248},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1979_248_4_a2/}
}