@article{MZ_1950__52_169112,
     author = {W. SCHWAN},
     title = {Zusammensetzung von {Schwesterperspektivit\"aten} in {Verb\"anden}},
     journal = {Mathematische Zeitschrift},
     pages = {150--167},
     publisher = {mathdoc},
     volume = {52},
     year = {1950},
     zbl = {0036.01701},
     url = {http://geodesic.mathdoc.fr/item/MZ_1950__52_169112/}
}