@article{MZ_1962__78_170033,
     author = {W. Greve},
     title = {Partial betweenness groups.},
     journal = {Mathematische Zeitschrift},
     pages = {305--318},
     year = {1962},
     volume = {78},
     zbl = {0104.02603},
     url = {http://geodesic.mathdoc.fr/item/MZ_1962__78_170033/}
}