@inproceedings{rené1955les,
title={Les congruences planes de coniques qui n'ont que deux points focaux},
author={René Lagrange},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203142720444816},
booktitle={Acta Mathematica},
volume={93},
number={1},
pages={257-292},
year={1955},
}
René Lagrange. Les congruences planes de coniques qui n'ont que deux points focaux. 1955. Vol. 93. In Acta Mathematica. pp.257-292. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203142720444816.