@article{MOMA_1962__66_177161,
     author = {Hans Robert M\"uller},
     title = {Zur {Geometrie} der {Strahlkongruenzen.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {161--165},
     publisher = {mathdoc},
     volume = {66},
     year = {1962},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1962__66_177161/}
}