@article{RM_1974_29_5_a0,
     author = {V. Ya. Ivrii and V. M. Petkov},
     title = {Necessary conditions for the {Cauchy} problem for non-strictly hyperbolic equations to be well-posed},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {1--70},
     publisher = {mathdoc},
     volume = {29},
     number = {5},
     year = {1974},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1974_29_5_a0/}
}