@incollection{JEDP_1976____A5_0, author = {Bolley, Pierre and Camus, Jacques and Helffer, Bernard}, title = {Remarques sur l'hypoellipticit\'e}, booktitle = {}, series = {Journ\'ees \'equations aux d\'eriv\'ees partielles}, eid = {5}, pages = {1--16}, publisher = {Ecole polytechnique}, year = {1976}, mrnumber = {54 #13290}, language = {fr}, url = {http://www.numdam.org/item/JEDP_1976____A5_0/} }