@article{MAN_1996__306_3_165457,
     author = {Bernhard Leeb and Michael Kapovich},
     title = {Actions of discrete groups on nonpositively curved spaces.},
     journal = {Mathematische Annalen},
     pages = {341--352},
     year = {1996},
     volume = {306},
     number = {3},
     zbl = {0856.20024},
     url = {http://geodesic.mathdoc.fr/item/MAN_1996__306_3_165457/}
}