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@article{MZ_1996__222_3_174878, author = {W. Ballmann and S. Buyalo}, title = {Nonpositively curved metrics on 2-polyhedra.}, journal = {Mathematische Zeitschrift}, pages = {97--134}, publisher = {mathdoc}, volume = {222}, number = {3}, year = {1996}, zbl = {0843.53036}, url = {http://geodesic.mathdoc.fr/item/MZ_1996__222_3_174878/} }
W. Ballmann; S. Buyalo. Nonpositively curved metrics on 2-polyhedra.. Mathematische Zeitschrift, Tome 222 (1996) no. 3, pp. 97-134. http://geodesic.mathdoc.fr/item/MZ_1996__222_3_174878/