@article{DE_1982_18_6_a9,
     author = {M. P. Grigolia},
     title = {A modified characteristic problem for hyperbolic systems with singularities},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1005--1014},
     year = {1982},
     volume = {18},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1982_18_6_a9/}
}