@incollection{JEDP_1980____A19_0,
     author = {Beals, Richard},
     title = {Propagation de singularit\'es pour les op\'erateurs du type $D^2_t-\square _b$},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {19},
     pages = {1--3},
     publisher = {Ecole polytechnique},
     year = {1980},
     zbl = {0454.58018},
     language = {fr},
     url = {http://www.numdam.org/item/JEDP_1980____A19_0/}
}