@inproceedings{orin1968subgroups,
title={Subgroups of IA automorphisms of a free group},
author={Orin Chein},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203217785268076},
booktitle={Acta Mathematica},
volume={123},
number={1},
pages={1-12},
year={1968},
}