@inproceedings{karl1969analyticity,
title={Analyticity of fundamental solutions},
author={Karl Gustav Andersson},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203443526646122},
booktitle={Arkiv for Matematik},
volume={8},
number={1},
pages={73-81},
year={1969},
}