@article{SEDP_1975-1976____A25_0,
     author = {Baouendi, M. S. and Sj\"ostrand, J.},
     title = {Non hypoellipticit\'e d'op\'erateurs elliptiques singuliers},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:24},
     pages = {1--7},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1975-1976},
     zbl = {0355.35018},
     language = {fr},
     url = {http://archive.numdam.org/item/SEDP_1975-1976____A25_0/}
}