@article{MAN_1961__142_160830,
     author = {G. LIEBOLD and O.-H. KELLER},
     title = {Bemerkungen zur {Inhaltslehre} der ebenen hyperbolischen {Geometrie.}},
     journal = {Mathematische Annalen},
     pages = {254--258},
     publisher = {mathdoc},
     volume = {142},
     year = {1961},
     zbl = {0094.33803},
     url = {http://geodesic.mathdoc.fr/item/MAN_1961__142_160830/}
}