@article{DAN_1966_170_6_a0,
     author = {I. V. Gel'man},
     title = {Stability of normally solvable extensions of partial differential operators},
     journal = {Doklady Akademii Nauk},
     pages = {1239--1242},
     publisher = {mathdoc},
     volume = {170},
     number = {6},
     year = {1966},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1966_170_6_a0/}
}