@article{DAN_1977_234_3_a9,
     author = {M. Otelbaev},
     title = {On the separability of elliptic operators},
     journal = {Doklady Akademii Nauk},
     pages = {540--543},
     publisher = {mathdoc},
     volume = {234},
     number = {3},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1977_234_3_a9/}
}