Fully nonlinear equations on Riemannian manifolds with negative curvature Matthew GurskyJeff Viaclovsky 35J6053C21fully nonlinear equationsRicci curvature Indiana University Mathematics Journal 2003 text pdf 10.1512/iumj.2003.52.2313 10.1512/iumj.2003.52.2313 en Indiana Univ. Math. J. 52 (2003) 399 - 420 state-of-the-art mathematics http://iumj.org/access/