@article{DE_1977_13_6_a14,
     author = {V. N. Vragov},
     title = {On the theory of boundary value problems for equations of mixed type in space},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1098--1105},
     publisher = {mathdoc},
     volume = {13},
     number = {6},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_6_a14/}
}