@inproceedings{patrick1981isometry,
title={Isometry groups of simply connected manifolds of nonpositive curvature II},
author={Patrick Eberlein},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203257698611321},
booktitle={Acta Mathematica},
volume={149},
number={1},
pages={41-69},
year={1981},
}
Patrick Eberlein. Isometry groups of simply connected manifolds of nonpositive curvature II. 1981. Vol. 149. In Acta Mathematica. pp.41-69. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203257698611321.