@article{RSMUP_1992__88__263_0,
     author = {Sordoni, V.},
     title = {Necessary and sufficient conditions for the well posedness of the {Cauchy} problem for a class of hyperbolic operators with high variable multiplicity},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {263--280},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {88},
     year = {1992},
     mrnumber = {1209129},
     zbl = {0815.35064},
     language = {en},
     url = {http://www.numdam.org/item/RSMUP_1992__88__263_0/}
}