TY  - JOUR
AU  - YanYan Li
AU  - Louis Nirenberg
TI  - A geometric problem and the Hopf Lemma. I
JO  - Journal of the European Mathematical Society
PY  - 2006
SP  - 317
EP  - 339
VL  - 8
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.4171/jems/55/
DO  - 10.4171/jems/55
ID  - JEMS_2006_8_2_a13
ER  -