@article{GDZPPN002398176,
title = {On Characteristic Subgroups of Free Groups.},
journal = {Mathematische Zeitschrift},
volume = {93},
year = {1966},
pages = {143-151},
zbl = {0143.03603},
url = {http://dml.mathdoc.fr/item/GDZPPN002398176}
}
Neumann, B.H. On Characteristic Subgroups of Free Groups.. Mathematische Zeitschrift, Tome 93 (1966) pp. 143-151. http://gdmltest.u-ga.fr/item/GDZPPN002398176/