@article{TSP_2006_25_25_a6,
     author = {O. I. Morozov},
     title = {Contact-equivalence problem for linear hyperbolic equations},
     journal = {Trudy Seminara im. I.G. Petrovskogo},
     pages = {119--142},
     publisher = {mathdoc},
     volume = {25},
     number = {25},
     year = {2006},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TSP_2006_25_25_a6/}
}