@article{AA_1993_5_1_a6,
     author = {S. V. Buyalo},
     title = {An example of a~four-dimensional manifold of negative curvature},
     journal = {Algebra i analiz},
     pages = {193--199},
     publisher = {mathdoc},
     volume = {5},
     number = {1},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1993_5_1_a6/}
}