@article{SEDP_1986-1987____A4_0,
     author = {Nourrigat, J.},
     title = {Syst\`emes sous-elliptiques},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:5},
     pages = {1--14},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1986-1987},
     mrnumber = {920023},
     zbl = {0635.35086},
     language = {fr},
     url = {http://archive.numdam.org/item/SEDP_1986-1987____A4_0/}
}