@article{MZ_1966__93_170580,
     author = {Armin Frei},
     title = {Freie {Objektive} und multiplikative {Strukturen.}},
     journal = {Mathematische Zeitschrift},
     pages = {109--141},
     publisher = {mathdoc},
     volume = {93},
     year = {1966},
     zbl = {0163.26701},
     url = {http://geodesic.mathdoc.fr/item/MZ_1966__93_170580/}
}