1. Department of MathematicsShaoxing University Shaoxing, Zhejiang China
2. Department of Computer Science, Royal HollowayUniversity of LondonEgham Surrey UK
3. Department of Mathematics and Computer ScienceUniversity of Southern DenmarkOdense Denmark
4. Department of Pure and Applied MathematicsUniversity of JohannesburgAuckland Park South Africa
5. School of Mathematical Science & Institute of MathematicsNanjing Normal University Nanjing, Jiangsu China