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