@inproceedings{pavel2007approximations,
title={Approximations of singular vertex couplings in quantum graphs},
author={Pavel Exner, and ONDEJ TUREK},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020123837066870597},
booktitle={Reviews in Mathematical Physics},
volume={19},
number={06},
pages={571-606},
year={2007},
}
Pavel Exner, and ONDEJ TUREK. Approximations of singular vertex couplings in quantum graphs. 2007. Vol. 19. In Reviews in Mathematical Physics. pp.571-606. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020123837066870597.