@article{IM_1986__85_143370,
     author = {V. Schroeder and M.T. Anderson},
     title = {Existence of flats in manifolds of nonpositive curvature.},
     journal = {Inventiones mathematicae},
     pages = {303--316},
     publisher = {mathdoc},
     volume = {85},
     year = {1986},
     zbl = {0615.53030},
     url = {http://geodesic.mathdoc.fr/item/IM_1986__85_143370/}
}