Affiliation: | 1. School of Mathematics and Statistics, Jiangsu Normal University, No. 101, Shanghai Road, Xuzhou 221116, Jiangsu, China;2. School of Mathematical Science, Tongji University, No. 1239, Siping Road, Yangpu District 200092, Shanghai, China;3. Department of Mathematics, National Tsing Hua University, No. 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan |