@article{AA_1991_3_4_a2,
     author = {S. V. Buyalo},
     title = {Homotopy invariance of some geometric properties of three-dimensional manifolds of nonpositive curvature},
     journal = {Algebra i analiz},
     pages = {93--112},
     year = {1991},
     volume = {3},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1991_3_4_a2/}
}