@article{DAN_1970_195_4_a5,
     author = {A. M. Nakhushev},
     title = {The {Darboux} problem for hyperbolic equations},
     journal = {Doklady Akademii Nauk},
     pages = {776--779},
     publisher = {mathdoc},
     volume = {195},
     number = {4},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_195_4_a5/}
}