@inproceedings{jan1970comparison,
title={Comparison theorems for a generalized modulus of continuity},
author={Jan Boman, and Harold S. Shapiro},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203446621516147},
booktitle={Arkiv for Matematik},
volume={9},
number={1},
pages={91-116},
year={1970},
}
Jan Boman, and Harold S. Shapiro. Comparison theorems for a generalized modulus of continuity. 1970. Vol. 9. In Arkiv for Matematik. pp.91-116. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203446621516147.