@inproceedings{motoo2000a,
title={A non-existence theorem of lacunas for hyperbolic differential operators with constant coefficients},
author={Motoo Uchida},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203604511195791},
booktitle={Arkiv for Matematik},
volume={40},
number={1},
pages={201-205},
year={2000},
}
Motoo Uchida. A non-existence theorem of lacunas for hyperbolic differential operators with constant coefficients. 2000. Vol. 40. In Arkiv for Matematik. pp.201-205. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203604511195791.