@article{AA_2001_13_4_a8,
     author = {P. V. Svetlov},
     title = {Metrics of nonpositive curvature on infinite graph-manifolds},
     journal = {Algebra i analiz},
     pages = {174--195},
     publisher = {mathdoc},
     volume = {13},
     number = {4},
     year = {2001},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_2001_13_4_a8/}
}