@article{JRAM_1939__180_150061,
     author = {Gerhard Kowalewski},
     title = {Zur nat\"urlichen {Geometrie} der irreduziblen {G7} von {Ber\"uhrungstransformationen.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {197--218},
     publisher = {mathdoc},
     volume = {180},
     year = {1939},
     zbl = {0021.25703},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1939__180_150061/}
}