@article{JEDP_1975____183_0,
     author = {Grigis, Alain},
     title = {Hypoellipticit\'e et param\'etrix pour des op\'erateurs pseudodiff\'erentiels \`a caract\'eristiques doubles},
     journal = {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/}
}