@article{MZ_1939__44_168800,
     author = {A. N., Rao},
     title = {On a principle of duality in circle sphere and line geometries},
     journal = {Mathematische Zeitschrift},
     pages = {185--194},
     year = {1939},
     volume = {44},
     zbl = {64.0656.02},
     url = {http://geodesic.mathdoc.fr/item/MZ_1939__44_168800/}
}