@article{DE_1974_10_8_a22,
     author = {Z. O. Mel'nik},
     title = {Hyperbolic equations with multiple characteristics},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1530--1532},
     publisher = {mathdoc},
     volume = {10},
     number = {8},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1974_10_8_a22/}
}