@article{DAN_1969_186_2_a6,
     author = {A. L. Chistyakov},
     title = {Deficiency indices of symmetric differential operators with polynomial coefficients},
     journal = {Doklady Akademii Nauk},
     pages = {268--271},
     publisher = {mathdoc},
     volume = {186},
     number = {2},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_186_2_a6/}
}