@inproceedings{yasutaka1967subdominant,
title={Subdominant solutions of the differential equation},
author={Yasutaka Sibuya},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203213682215047},
booktitle={Acta Mathematica},
volume={119},
number={1},
pages={235-272},
year={1967},
}