1. School of Mathematics, Iran University of Science and Technology, Tehran 13114-16846 Iran (e-mail: ahmadi_reza@iust.ac.ir).
2. Kent Business School, University of Kent, Canterbury CT2 7FS U.K. (e-mail: S.M.Wu@kent.ac.uk).
3. Department of Mathematics, Statistics, and Computer Science, Semnan University, Semnan 19111-35131 Iran (e-mail: a_sobhani@semnan.ac.ir).