@article{JEDP_1980____A9_0,
     author = {Maire, Henri-Michel},
     title = {Sous-ellipticit\'e et hypoellipticit\'e maximale pour des syst\`emes diff\'erentiels},
     journal = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {9},
     pages = {1--2},
     publisher = {Ecole polytechnique},
     year = {1980},
     zbl = {0444.35020},
     language = {fr},
     url = {http://www.numdam.org/item/JEDP_1980____A9_0/}
}