@incollection{JEDP_1976____A14_0, author = {Rolland, Jacques}, title = {Hypoellipticit\'e partielle pour des op\'erateurs elliptiques et d\'eg\'en\'er\'es}, booktitle = {}, series = {Journ\'ees \'equations aux d\'eriv\'ees partielles}, eid = {14}, pages = {1--29}, publisher = {Ecole polytechnique}, year = {1976}, language = {fr}, url = {http://archive.numdam.org/item/JEDP_1976____A14_0/} }