Symmetry Diffeomorphism Group of a Manifold of Nonpositive Curvature, II Patrick Eberlein Indiana University Mathematics Journal 1988 text pdf 10.1512/iumj.1988.37.37036 10.1512/iumj.1988.37.37036 en Indiana Univ. Math. J. 37 (1988) 735 - 752 state-of-the-art mathematics http://iumj.org/access/