@inproceedings{lars1979on,
title={On the asymptotic distribution of the eigenvalues of pseudodifferential operators in$R$^{$n$}},
author={Lars Hörmander},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203507167951323},
booktitle={Arkiv for Matematik},
volume={17},
number={1},
pages={297-313},
year={1979},
}
Lars Hörmander. On the asymptotic distribution of the eigenvalues of pseudodifferential operators in$R$^{$n$}. 1979. Vol. 17. In Arkiv for Matematik. pp.297-313. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203507167951323.