@article{DAN_1989_305_6_a7,
     author = {Ya. A. Roitberg and Z. G. Sheftel},
     title = {On the denseness of solutions to elliptic problems with localized},
     journal = {Doklady Akademii Nauk},
     pages = {1317--1320},
     publisher = {mathdoc},
     volume = {305},
     number = {6},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_305_6_a7/}
}