@article{DAN_1972_204_6_a5,
     author = {V. Ya. Ivrii},
     title = {The {Cauchy} problem for nonstrictly hyperbolic equations with smooth roots},
     journal = {Doklady Akademii Nauk},
     pages = {1303--1304},
     publisher = {mathdoc},
     volume = {204},
     number = {6},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1972_204_6_a5/}
}