@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},
     address = {Grenoble},
     volume = {24},
     number = {1},
     year = {1974},
     doi = {10.5802/aif.499},
     mrnumber = {50 #2726},
     zbl = {0273.35058},
     language = {en},
     url = {http://www.numdam.org/articles/10.5802/aif.499/}
}