@article{AIF_1976__26_1_141_0,
     author = {Sj\"ostrand, Johannes},
     title = {Propagation of singularities for operators with multiple involutive characteristics},
     journal = {Annales de l'Institut Fourier},
     pages = {141--155},
     publisher = {Institut Fourier},
     address = {Grenoble},
     volume = {26},
     number = {1},
     year = {1976},
     doi = {10.5802/aif.602},
     mrnumber = {54 #13285},
     zbl = {0313.58021},
     language = {en},
     url = {http://www.numdam.org/articles/10.5802/aif.602/}
}