@article{IM2_1974_8_4_a5,
     author = {Yu. L. Shmul'yan},
     title = {Extension theory for operators and spaces with indefinite metric},
     journal = {Izvestiya. Mathematics },
     pages = {895--907},
     publisher = {mathdoc},
     volume = {8},
     number = {4},
     year = {1974},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1974_8_4_a5/}
}