@article{JEDP_1976____A5_0,
     author = {Bolley, Pierre and Camus, Jacques and Helffer, Bernard},
     title = {Remarques sur l'hypoellipticit\'e},
     journal = {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://archive.numdam.org/item/JEDP_1976____A5_0/}
}