@inproceedings{trygve1961on,
title={On the sum of two integral squares in certain quadratic fields},
author={Trygve Nagell},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203426314848974},
booktitle={Arkiv for Matematik},
volume={4},
number={2},
pages={267-286},
year={1961},
}