@article{SEDP_1979-1980____A1_0,
     author = {Helffer, B.},
     title = {Hypoellipticit\'e analytique sur des groupes nilpotents de rang $2$ (d{\textquoteright}apr\`es {G.} {Metivier)}},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:1},
     pages = {1--13},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1979-1980},
     mrnumber = {600685},
     zbl = {0471.35022},
     language = {fr},
     url = {http://archive.numdam.org/item/SEDP_1979-1980____A1_0/}
}