@article{AA_1999_11_2_a2,
     author = {S. V. Buyalo and V. L. Kobel'skii},
     title = {Generalized graph-manifolds of nonpositive curvature},
     journal = {Algebra i analiz},
     pages = {64--87},
     publisher = {mathdoc},
     volume = {11},
     number = {2},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1999_11_2_a2/}
}