@article{MZ_1966__93_170576,
     author = {Oskar Perron},
     title = {Kreisverwandtschaften in der hyperbolischen {Geometrie.}},
     journal = {Mathematische Zeitschrift},
     pages = {69--79},
     publisher = {mathdoc},
     volume = {93},
     year = {1966},
     zbl = {0138.41605},
     url = {http://geodesic.mathdoc.fr/item/MZ_1966__93_170576/}
}