@inproceedings{alf1977the,
title={The trace of potentials on general sets},
author={Alf Jonsson},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203504502044301},
booktitle={Arkiv for Matematik},
volume={17},
number={1},
pages={1-18},
year={1977},
}