@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://geodesic.mathdoc.fr/item/JEDP_1976____A14_0/}
}