@article{JRAM_1981__327_152381,
     author = {Robert Shelton},
     title = {Aperiodic words on three symbols. {II.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {1--11},
     publisher = {mathdoc},
     volume = {327},
     year = {1981},
     zbl = {0455.05014},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1981__327_152381/}
}