@inproceedings{r.1970the,
title={The center and the commutator subgroup in hopfian groups},
author={R. Hirshon},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203447213535152},
booktitle={Arkiv for Matematik},
volume={9},
number={1},
pages={181-192},
year={1970},
}