@article{DAN_1987_293_2_a8,
     author = {N. Yu. Kapustin},
     title = {On two problems for a hyperbolic equation in the characteristic},
     journal = {Doklady Akademii Nauk},
     pages = {301--305},
     publisher = {mathdoc},
     volume = {293},
     number = {2},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1987_293_2_a8/}
}