@article{MAN_1986__274_164083,
     author = {Viktor Schroeder},
     title = {Rigidity of {Nonpositively} {Curved} {Graphmanifolds.}},
     journal = {Mathematische Annalen},
     pages = {19--26},
     publisher = {mathdoc},
     volume = {274},
     year = {1986},
     zbl = {0591.53038},
     url = {http://geodesic.mathdoc.fr/item/MAN_1986__274_164083/}
}