@inproceedings{s.1970necessary,
title={Necessary and sufficient conditions for the hyperbolicity of polynomials with hyperbolic principal part},
author={S. Leif Svensson},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203444407808130},
booktitle={Arkiv for Matematik},
volume={8},
number={2},
pages={145-162},
year={1970},
}
S. Leif Svensson. Necessary and sufficient conditions for the hyperbolicity of polynomials with hyperbolic principal part. 1970. Vol. 8. In Arkiv for Matematik. pp.145-162. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203444407808130.