1. College of Science, Lorestan University, Lorestan, Khoramabad, Iran
2. Department of Mathematical Sciences, Purdue University Fort Wayne, Fort Wayne, Indiana, USA
3. School of Computer Science, University of Oklahoma, Norman, Oklahoma, USA
4. Department of Mathematics, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
5. Department of Mathematics, College of Sciences, Shiraz University, Shiraz, Iran