@article{MZ_1986__192_173739, author = {V. Schroeder}, title = {On the {Fundamental} {Group} of a {Visibility} {Manifold.}}, journal = {Mathematische Zeitschrift}, pages = {347--352}, publisher = {mathdoc}, volume = {192}, year = {1986}, zbl = {0596.53035}, url = {http://geodesic.mathdoc.fr/item/MZ_1986__192_173739/} }