@article{DAN_1970_192_3_a8,
     author = {Ya. A. Roitberg and Z. G. Sheftel},
     title = {A certain class of general nonlocal elliptic problems},
     journal = {Doklady Akademii Nauk},
     pages = {511--513},
     publisher = {mathdoc},
     volume = {192},
     number = {3},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_192_3_a8/}
}