@article{IM_1995__122_3_144321,
     author = {Bernhard Leeb},
     title = {3-manifolds with(out) metrics of nonpositive curvature.},
     journal = {Inventiones mathematicae},
     pages = {277--290},
     publisher = {mathdoc},
     volume = {122},
     number = {3},
     year = {1995},
     zbl = {0840.53031},
     url = {http://geodesic.mathdoc.fr/item/IM_1995__122_3_144321/}
}