@incollection{JEDP_1977____81_0,
     author = {Hardin, T. and Laville},
     title = {Une g\'en\'eralisation du th\'eor\`eme de propagation des singularit\'es pour les op\'erateurs \`a symbole principal r\'eel},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     pages = {81--87},
     publisher = {Ecole polytechnique},
     year = {1977},
     mrnumber = {81j:35113},
     zbl = {0388.35004},
     language = {fr},
     url = {http://archive.numdam.org/item/JEDP_1977____81_0/}
}