@incollection{JEDP_1980____A9_0, author = {Maire, Henri-Michel}, title = {Sous-ellipticit\'e et hypoellipticit\'e maximale pour des syst\`emes diff\'erentiels}, booktitle = {}, series = {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/} }