@article{PIM_1950_S_S_III_03_a6,
     author = {L. Locher-Ernst},
     title = {Polarsysteme {Und} {Damit} {Zusammenh\"angende} {Ber\"uhrungstransformationen.} {Das} {Prinzip} {Von} {Hygens} {In} {Der} {Nichteuklidischen} {Geometrie}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {101 },
     publisher = {mathdoc},
     volume = {_S_S_III},
     number = {03},
     year = {1950},
     url = {http://geodesic.mathdoc.fr/item/PIM_1950_S_S_III_03_a6/}
}