@article{DAN_1971_201_1_a10,
     author = {V. S. Shulman},
     title = {On algebras of operators in a space with indefinite metric of type $\Pi_1$},
     journal = {Doklady Akademii Nauk},
     pages = {44--47},
     year = {1971},
     volume = {201},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1971_201_1_a10/}
}