@article{DAN_1966_169_1_a1,
     author = {G. K. Langer},
     title = {Invariant subspaces of linear operators acting in a space with indefinite metric},
     journal = {Doklady Akademii Nauk},
     pages = {12--15},
     publisher = {mathdoc},
     volume = {169},
     number = {1},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1966_169_1_a1/}
}