@article{DE_1972_8_5_a11,
     author = {P. P. Zabreiko and Yu. I. Fetisov},
     title = {The method of a small parameter for hyperbolic equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {823--834},
     publisher = {mathdoc},
     volume = {8},
     number = {5},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_5_a11/}
}