@article{DAN_1962_143_3_a2,
     author = {M. Sh. Birman},
     title = {On existence conditions for wave operators},
     journal = {Doklady Akademii Nauk},
     pages = {506--509},
     publisher = {mathdoc},
     volume = {143},
     number = {3},
     year = {1962},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1962_143_3_a2/}
}