@incollection{JEDP_1990____A9_0, author = {Dencker, Nils}, title = {Preparation theorems for systems}, booktitle = {}, series = {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/} }