@article{DE_1981_17_1_a4,
     author = {N. N. Gaidai},
     title = {Existence of the spectrum for the {Tricomi} operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {31--38},
     publisher = {mathdoc},
     volume = {17},
     number = {1},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1981_17_1_a4/}
}