@article{PMIHES_1995__82__169_0,
     author = {Ballmann, Werner and Brin, Michael},
     title = {Orbihedra of nonpositive curvature},
     journal = {Publications Math\'ematiques de l'IH\'ES},
     pages = {169--209},
     publisher = {Institut des Hautes \'Etudes Scientifiques},
     volume = {82},
     year = {1995},
     mrnumber = {97i:53049},
     zbl = {0866.53029},
     language = {en},
     url = {http://www.numdam.org/item/PMIHES_1995__82__169_0/}
}