@article{SLC_1984_10_a9,
     author = {Jean Berstel},
     title = {W\"orter ohne {Wiederholungen}},
     journal = {S\'eminaire lotharingien de combinatoire},
     year = {1984},
     volume = {10},
     url = {http://geodesic.mathdoc.fr/item/SLC_1984_10_a9/}
}