@article{DAN_1977_232_5_a4,
     author = {V. V. Kolobaev and \`E. M. Saak},
     title = {On a class of hyperbolic systems},
     journal = {Doklady Akademii Nauk},
     pages = {1000--1003},
     publisher = {mathdoc},
     volume = {232},
     number = {5},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1977_232_5_a4/}
}