@inproceedings{peter1981on,
title={On the comparison principle in the calculus of variations},
author={Peter Lindqvist},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203515282849392},
booktitle={Arkiv for Matematik},
volume={21},
number={1},
pages={185-190},
year={1981},
}