@inproceedings{ulf1947determination,
title={Determination of the denominator of Fredholm in some types of integral equations},
author={Ulf Hellsten},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203122918339671},
booktitle={Acta Mathematica},
volume={79},
number={1},
pages={105-152},
year={1947},
}
Ulf Hellsten. Determination of the denominator of Fredholm in some types of integral equations. 1947. Vol. 79. In Acta Mathematica. pp.105-152. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203122918339671.