@inproceedings{pavel1996weakly,
title={Weakly coupled states on branching graphs},
author={Pavel Exner},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020122901313664573},
booktitle={Letters in Mathematical Physics},
volume={38},
number={3},
pages={313-320},
year={1996},
}

Pavel Exner. Weakly coupled states on branching graphs. 1996. Vol. 38. In Letters in Mathematical Physics. pp.313-320. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020122901313664573.