@article{AIF_1974__24_1_225_0, author = {Cardoso, Fernando and Tr\`eves, Fran\c{c}ois}, title = {A necessary condition of local solvability for pseudo-differential equations with double characteristics}, journal = {Annales de l'Institut Fourier}, pages = {225--292}, publisher = {Institut Fourier}, volume = {24}, number = {1}, year = {1974}, doi = {10.5802/aif.499}, zbl = {0273.35058}, mrnumber = {50 #2726}, language = {en}, url = {http://www.numdam.org/articles/10.5802/aif.499/} }