%0 Journal Article
%A YanYan Li
%A Louis Nirenberg
%T A geometric problem and the Hopf Lemma. I
%J Journal of the European Mathematical Society
%D 2006
%P 317-339
%V 8
%N 2
%I mathdoc
%U http://geodesic.mathdoc.fr/articles/10.4171/jems/55/
%R 10.4171/jems/55
%F JEMS_2006_8_2_a13