@article{DE_1994_30_4_a20,
     author = {N. A. Sidorov and O. A. Romanova and E. B. Blagodatskaya},
     title = {Partial differential equations with an operator of finite index at the principal part},
     journal = {Differencialʹnye uravneni\^a},
     pages = {729--731},
     publisher = {mathdoc},
     volume = {30},
     number = {4},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1994_30_4_a20/}
}