@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/