@article{SEDP_1981-1982____A11_0,
     author = {M\'etivier, G.},
     title = {Non hypoellipticit\'e analytique pour des op\'erateurs \`a caract\'eristiques doubles},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:12},
     pages = {1--12},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1981-1982},
     mrnumber = {671609},
     zbl = {0489.35033},
     language = {fr},
     url = {http://www.numdam.org/item/SEDP_1981-1982____A11_0/}
}