@inproceedings{werner1960jakob,
title={Jakob Nielsen in memoriam},
author={Werner Fenchel},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203154229890902},
booktitle={Acta Mathematica},
volume={103},
number={3},
pages={IV-XIX},
year={1960},
}