@inproceedings{pekka1991removability,
title={Removability theorems for solutions of degenerate elliptic partial differential equations},
author={Pekka Koskela, and Olli Martio},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203541222005608},
booktitle={Arkiv for Matematik},
volume={31},
number={2},
pages={339-353},
year={1991},
}
Pekka Koskela, and Olli Martio. Removability theorems for solutions of degenerate elliptic partial differential equations. 1991. Vol. 31. In Arkiv for Matematik. pp.339-353. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203541222005608.