@inproceedings{jouko1987on,
title={On essential maximality of linear pseudo-differential operators},
author={Jouko Tervo},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203530910841522},
booktitle={Arkiv for Matematik},
volume={27},
number={1},
pages={343-361},
year={1987},
}