@article{DAN_1970_192_6_a9,
     author = {R. L. Frum-Ketkov},
     title = {Mappings in {Hilbert} space},
     journal = {Doklady Akademii Nauk},
     pages = {1231--1234},
     publisher = {mathdoc},
     volume = {192},
     number = {6},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_192_6_a9/}
}