@article{GDZPPN002179768,
title = {Dependence and Independence in Free Groups.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {211},
year = {1962},
pages = {148-174},
zbl = {0105.01901},
url = {http://dml.mathdoc.fr/item/GDZPPN002179768}
}
Lyndon, Roger C. Dependence and Independence in Free Groups.. Journal für die reine und angewandte Mathematik, Tome 211 (1962) pp. 148-174. http://gdmltest.u-ga.fr/item/GDZPPN002179768/