@article{AA_2003_15_1_a1,
     author = {S. V. Buyalo},
     title = {Estimation of the volume entropy for graph-manifolds of nonpositive curvature},
     journal = {Algebra i analiz},
     pages = {63--72},
     publisher = {mathdoc},
     volume = {15},
     number = {1},
     year = {2003},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_2003_15_1_a1/}
}