@incollection{JEDP_1976____A13_0, author = {Pham The Lai}, title = {Th\'eorie spectrale d'une classe d'op\'erateurs diff\'erentiels hypoelliptiques}, booktitle = {}, series = {Journ\'ees \'equations aux d\'eriv\'ees partielles}, eid = {13}, pages = {1--59}, publisher = {Ecole polytechnique}, year = {1976}, language = {fr}, url = {http://archive.numdam.org/item/JEDP_1976____A13_0/} }