TY - JOUR AU - Sjöstrand, Johannes TI - Propagation of singularities for operators with multiple involutive characteristics JO - Annales de l'Institut Fourier PY - 1976 SP - 141 EP - 155 VL - 26 IS - 1 PB - Institut Fourier PP - Grenoble UR - https://aif.centre-mersenne.org/articles/10.5802/aif.602/ DO - 10.5802/aif.602 LA - en ID - AIF_1976__26_1_141_0 ER -