@article{GDZPPN002103079,
title = {Existence of flats in manifolds of nonpositive curvature.},
journal = {Inventiones mathematicae},
volume = {83},
year = {1986},
pages = {303-316},
zbl = {0615.53030},
url = {http://dml.mathdoc.fr/item/GDZPPN002103079}
}
Schroeder, V.; Anderson, M.T. Existence of flats in manifolds of nonpositive curvature.. Inventiones mathematicae, Tome 83 (1986) pp. 303-316. http://gdmltest.u-ga.fr/item/GDZPPN002103079/