@article{DE_1978_14_1_a12,
     author = {S. S. Kharibegashvili},
     title = {The characteristic problem for second-order hyperbolic systems with constant coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {123--135},
     publisher = {mathdoc},
     volume = {14},
     number = {1},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1978_14_1_a12/}
}