@incollection{JEDP_1995____A9_0,
     author = {Christ, Michael},
     title = {On local and global analytic and {Gevrey} hypoellipticity},
     booktitle = {},
     series = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {9},
     pages = {1--7},
     publisher = {Ecole polytechnique},
     year = {1995},
     mrnumber = {96h:35029},
     zbl = {0881.35026},
     language = {en},
     url = {http://archive.numdam.org/item/JEDP_1995____A9_0/}
}