@article{DE_1982_18_11_a21,
     author = {A. V. Knyazev},
     title = {Differential operators with nonrational characteristics},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1986--1989},
     publisher = {mathdoc},
     volume = {18},
     number = {11},
     year = {1982},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1982_18_11_a21/}
}