@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/}
}