@article{DE_1977_13_1_a16,
     author = {V. I. Pa\v{s}kovskii},
     title = {Connected partial differential operators with different principal parts},
     journal = {Differencialʹnye uravneni\^a},
     pages = {121--125},
     publisher = {mathdoc},
     volume = {13},
     number = {1},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_1_a16/}
}