@article{GDZPPN002322102,
title = {A Canonical Form for Compact Nonpositively Curved Manifolds Whose Fundamental Groups Have Nontrivial Center.},
journal = {Mathematische Annalen},
volume = {261},
year = {1982},
pages = {23-30},
zbl = {0468.57014},
url = {http://dml.mathdoc.fr/item/GDZPPN002322102}
}
Eberlein, Patrick. A Canonical Form for Compact Nonpositively Curved Manifolds Whose Fundamental Groups Have Nontrivial Center.. Mathematische Annalen, Tome 261 (1982) pp. 23-30. http://gdmltest.u-ga.fr/item/GDZPPN002322102/