@inproceedings{einar1967on,
title={On the existence of the scattering operator},
author={Einar Lundqvist},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203438313881076},
booktitle={Arkiv for Matematik},
volume={7},
number={2},
pages={145-157},
year={1967},
}