%0 Journal Article %A Sjöstrand, Johannes %T Propagation of singularities for operators with multiple involutive characteristics %J Annales de l'Institut Fourier %D 1976 %P 141-155 %V 26 %N 1 %I Institut Fourier %U https://doi.org/10.5802/aif.602 %R 10.5802/aif.602 %G en %F AIF_1976__26_1_141_0