@article{JEDP_1990____A9_0,
     author = {Dencker, Nils},
     title = {Preparation theorems for systems},
     journal = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {9},
     pages = {1--10},
     publisher = {Ecole polytechnique},
     year = {1990},
     mrnumber = {91g:32008},
     zbl = {0716.58006},
     language = {en},
     url = {http://www.numdam.org/item/JEDP_1990____A9_0/}
}