@incollection{JEDP_1978____A2_0,
     author = {Sj\"ostrand, Johannes},
     title = {Valeurs propres pour des op\'erateurs hypoelliptique},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {2},
     pages = {1--2},
     publisher = {Ecole polytechnique},
     year = {1978},
     language = {fr},
     url = {http://archive.numdam.org/item/JEDP_1978____A2_0/}
}