@article{ITA_1986__20_1_47_0,
     author = {Harju, Tero and Linna, Matti},
     title = {On the periodicity of morphisms on free monoids},
     journal = {RAIRO - Theoretical Informatics and Applications - Informatique Th\'eorique et Applications},
     pages = {47--54},
     publisher = {AFCET - Gauthier-Villars},
     address = {Paris},
     volume = {20},
     number = {1},
     year = {1986},
     mrnumber = {849965},
     zbl = {0608.68065},
     language = {en},
     url = {http://www.numdam.org/item/ITA_1986__20_1_47_0/}
}