@article{PSMIR_1976___1_A6_0,
     author = {Bolley, P. and Camus, J. and Helffer, B.},
     title = {Remarques sur l'hypoellipticit\'e},
     journal = {Publications de l'Institut de recherche math\'ematiques de Rennes},
     eid = {6},
     pages = {1--16},
     publisher = {D\'epartement de Math\'ematiques et Informatique, Universit\'e de Rennes},
     number = {1},
     year = {1976},
     language = {fr},
     url = {http://geodesic.mathdoc.fr/item/PSMIR_1976___1_A6_0/}
}