@incollection{JEDP_1975____183_0, author = {Grigis, Alain}, title = {Hypoellipticit\'e et param\'etrix pour des op\'erateurs pseudodiff\'erentiels \`a caract\'eristiques doubles}, booktitle = {}, series = {Journ\'ees \'equations aux d\'eriv\'ees partielles}, pages = {183--205}, publisher = {Ecole polytechnique}, year = {1975}, language = {fr}, url = {http://www.numdam.org/item/JEDP_1975____183_0/} }