@article{DAN_1966_170_1_a7,
     author = {M. G. Krein and Yu. L. Shmul'yan},
     title = {A class of operators in a space with an indefinite metric},
     journal = {Doklady Akademii Nauk},
     pages = {34--37},
     publisher = {mathdoc},
     volume = {170},
     number = {1},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1966_170_1_a7/}
}