@article{SM_1985_50_1_a8,
     author = {S. V. Buyalo},
     title = {Volume and fundamental group of a~manifold of nonpositive curvature},
     journal = {Sbornik. Mathematics},
     pages = {137--150},
     year = {1985},
     volume = {50},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1985_50_1_a8/}
}