1. Department of Mathematics, University of Houston, Houston, TX 77204, USA
2. Department of Computing and Mathematical Sciences, Cameron University, Lawton, OK 73505, USA
3. Department of Mathematics, Hans Raj Mahila Mahavidyalaya, Jalandhar 144008, Punjab, India
4. Department of Mathematics, Indira Gandhi National Tribal University, Lalpur, Markantak, Annuppur 484887, Madhya Pradesh, India