@inproceedings{clas1971the,
title={The asymptotic distribution of the eigenvalues of a degenerate elliptic operator},
author={Clas Nordin},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203448264304161},
booktitle={Arkiv for Matematik},
volume={10},
number={1},
pages={9-21},
year={1971},
}
Clas Nordin. The asymptotic distribution of the eigenvalues of a degenerate elliptic operator. 1971. Vol. 10. In Arkiv for Matematik. pp.9-21. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203448264304161.