1. Lihui Tian and Guanying Wang are at the Institute of Finance and Development; Nankai University; Tianjin China
2. Xingchun Wang and Yongjin Wang are at the School of Mathematical Sciences and LPMC; Nankai University; Tianjin China
3. Xingchun Wang is also at the Mathematical Institute; University of Oxford; Oxford UK
4. Yongjin Wang is also at the School of Business; Nankai University; Tianjin China