@inproceedings{jinzhi2016on,
title={On a classification of polynomial differential operators with respect to the type of first integrals},
author={Jinzhi Lei},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170210160838471535428},
booktitle={Journal of Differential Equations},
volume={260},
pages={1993-2005},
year={2016},
}

Jinzhi Lei. On a classification of polynomial differential operators with respect to the type of first integrals. 2016. Vol. 260. In Journal of Differential Equations. pp.1993-2005. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170210160838471535428.