@inproceedings{wolfgang1979on,
title={On the regularity of difference schemes},
author={Wolfgang Hackbusch},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203509620689344},
booktitle={Arkiv for Matematik},
volume={19},
number={1},
pages={71-95},
year={1979},
}