@inproceedings{david2005area,,
title={Area, coarea, and approximation in$W$^{1,1}},
author={David Swanson},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203620972096924},
booktitle={Arkiv for Matematik},
volume={45},
number={2},
pages={381-399},
year={2005},
}