@ARTICLE {33333,
author={D. Graça and N. Zhong},
doi={10.1090/tran/8644},
journal={Transactions of the American Mathematical Society},
title={Computing the exact number of periodic orbits for planar flows},
year={2022},
month={May},
volume={375},
number={08},
pages={5491-5538},
ISSN={0002-9947}
}