TY  - JOUR
AU  - Udo Simon
TI  - On differential operators of second order on Riemannian manifolds with nonpositive curvature
JO  - Colloquium Mathematicum
PY  - 1974
SP  - 223
EP  - 229
VL  - 31
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.4064/cm-31-2-223-229/
DO  - 10.4064/cm-31-2-223-229
LA  - en
ID  - 10_4064_cm_31_2_223_229
ER  -