@article{SEDP_1987-1988____A19_0,
     author = {Vaillant, J.},
     title = {Conditions d'hyperbolicit\'e pour les syst\`emes \`a multiplicit\'e constante, de rang pouvant varier},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:19},
     pages = {1--11},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1987-1988},
     mrnumber = {1018191},
     zbl = {0684.35006},
     language = {fr},
     url = {http://www.numdam.org/item/SEDP_1987-1988____A19_0/}
}