@inproceedings{karlheinz1998nonperiodic,
title={Nonperiodic sampling and the local three squares theorem},
author={Karlheinz Gröchenig, Christopher Heil, and David Walnut},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203558101508740},
booktitle={Arkiv for Matematik},
volume={38},
number={1},
pages={77-92},
year={1998},
}

Karlheinz Gröchenig, Christopher Heil, and David Walnut. Nonperiodic sampling and the local three squares theorem. 1998. Vol. 38. In Arkiv for Matematik. pp.77-92. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203558101508740.