@article{DE_1976_12_5_a9,
     author = {Yu. L. Daletskii and E. A. Fadeeva},
     title = {Hyperbolic equations with variable operator-valued coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {881--891},
     publisher = {mathdoc},
     volume = {12},
     number = {5},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1976_12_5_a9/}
}