@article{JRAM_1960__204_150433,
     author = {J. Dieudonn\'e},
     title = {Sur une propri\'et\'e des groupes libres.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {30--34},
     year = {1960},
     volume = {204},
     zbl = {0098.02402},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1960__204_150433/}
}