@article{ELMA_1988__43_3_141431,
     author = {Helmut Sieber},
     title = {Ein elementargeometrischer {Beweis} des {Lotensatzes} von {Hjelmslev.}},
     journal = {Elemente der Mathematik},
     pages = {86--88},
     publisher = {mathdoc},
     volume = {43},
     number = {3},
     year = {1988},
     zbl = {0709.51016},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1988__43_3_141431/}
}