@inproceedings{simon2000on,
title={On the complexity of the classification problem for torsion-free abelian groups of rank two},
author={Simon Thomas},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203341474639632},
booktitle={Acta Mathematica},
volume={189},
number={2},
pages={287-305},
year={2000},
}
Simon Thomas. On the complexity of the classification problem for torsion-free abelian groups of rank two. 2000. Vol. 189. In Acta Mathematica. pp.287-305. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203341474639632.