Partial results on extending the Hopf Lemma
Yanyan Li, Louis Nirenberg · arXiv (Cornell University) · 2009
In [1], Theorem 3, the authors proved, in one dimension, a generalization of the Hopf Lemma, and the question arose if it could be extended to higher dimensions. In this paper we present two conjectures as possible extensions, and give a very partial answer. We write this paper to call attention to the problem.