@incollection{JEDP_1977____88_0, author = {Helffer, Bernard}, title = {Quelques exemples d'op\'erateurs pseudodiff\'erentiels localement r\'esolubles}, booktitle = {}, series = {Journ\'ees \'equations aux d\'eriv\'ees partielles}, pages = {88--116}, publisher = {Ecole polytechnique}, year = {1977}, mrnumber = {81g:58035}, zbl = {0388.47031}, language = {fr}, url = {http://archive.numdam.org/item/JEDP_1977____88_0/} }