@article{10_2140_agt_2004_4_603,
     author = {Xie, Xiangdong},
     title = {Foldable cubical complexes of nonpositive curvature},
     journal = {Algebraic and Geometric Topology},
     pages = {603--622},
     year = {2004},
     volume = {4},
     number = {1},
     doi = {10.2140/agt.2004.4.603},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2004.4.603/}
}