@article{DE_1984_20_2_a13,
     author = {A. A. Borgardt and D. Ya. Karpenko},
     title = {Characteristic problem for the massive wave equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {302--308},
     publisher = {mathdoc},
     volume = {20},
     number = {2},
     year = {1984},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1984_20_2_a13/}
}