@article{DE_1978_14_1_a8,
     author = {N. I. Popivanov},
     title = {A multidimensional analogue of the {Darboux} problem for degenerate hyperbolic equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {80--93},
     publisher = {mathdoc},
     volume = {14},
     number = {1},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1978_14_1_a8/}
}