@inproceedings{david1997sobolev,
title={Sobolev functions whose inner trace at the boundary is zero},
author={David Swanson, and William P. Ziemer},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203556783693731},
booktitle={Arkiv for Matematik},
volume={37},
number={2},
pages={373-380},
year={1997},
}
David Swanson, and William P. Ziemer. Sobolev functions whose inner trace at the boundary is zero. 1997. Vol. 37. In Arkiv for Matematik. pp.373-380. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203556783693731.