@article{DE_1969_5_1_a5,
     author = {M. M. Zainulabidov},
     title = {Certain boundary value problems for equations of mixed type with two perpendicular lines of degeneracy},
     journal = {Differencialʹnye uravneni\^a},
     pages = {91--99},
     year = {1969},
     volume = {5},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_1_a5/}
}