@incollection{JEDP_1979____A10_0,
     author = {Bernard Helffer and Jean Nourrigat},
     title = {Hypoellipticit\'e pour des op\'erateurs quasi-homog\`enes \`a coefficients polynomiaux},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {10},
     pages = {1--5},
     publisher = {\'Ecole polytechnique},
     year = {1979},
     zbl = {0405.35024},
     mrnumber = {83c:35026},
     language = {fr},
     url = {https://proceedings.centre-mersenne.org/item/JEDP_1979____A10_0/}
}