@article{DE_1969_5_12_a15,
     author = {I. V. Gel'man},
     title = {A certain characteristic of normally solvable extensions of a minimal operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2274--2275},
     publisher = {mathdoc},
     volume = {5},
     number = {12},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_12_a15/}
}