@article{SEDP_1979-1980____A12_0,
     author = {Melrose, R. B.},
     title = {Hypoelliptic operators with characteristic variety of codimension two and the wave equation},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:11},
     pages = {1--12},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1979-1980},
     mrnumber = {600696},
     zbl = {0468.35032},
     language = {en},
     url = {http://www.numdam.org/item/SEDP_1979-1980____A12_0/}
}