@article{IM2_1987_28_2_a1,
     author = {V. A. Vassiliev},
     title = {Sharpness and the local {Petrovskii} condition for strictly hyperbolic operators with constant coefficients},
     journal = {Izvestiya. Mathematics },
     pages = {233--273},
     publisher = {mathdoc},
     volume = {28},
     number = {2},
     year = {1987},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1987_28_2_a1/}
}