@article{DAN_1962_146_6_a7,
     author = {Ya. A. Roitberg and Z. G. Sheftel},
     title = {On equations of elliptic type with discontinuous coefficients},
     journal = {Doklady Akademii Nauk},
     pages = {1275--1278},
     publisher = {mathdoc},
     volume = {146},
     number = {6},
     year = {1962},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1962_146_6_a7/}
}