@inproceedings{fei2010gravitational, title={Gravitational anomaly cancellation and modular invariance}, author={Fei Han, and Kefeng Liu}, url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191221111612903104670}, booktitle={arXiv preprint arXiv:1007.5295}, year={2010}, }