@article{1077374788,
author = {Crowell, R. H.},
title = {The group $G'/G''$ of a knot group $G$},
journal = {Duke Math. J.},
volume = {30},
number = {1},
year = {1963},
pages = { 349-354},
language = {en},
url = {http://dml.mathdoc.fr/item/1077374788}
}
Crowell, R. H. The group $G'/G''$ of a knot group $G$. Duke Math. J., Tome 30 (1963) no. 1, pp. 349-354. http://gdmltest.u-ga.fr/item/1077374788/