1. Department of Mathematics, Jaypee Institute of Information Technology, Deemed University, A-10, Sector-62, Noida-201307 (UP), India
2. Department of Applied Mathematics, Institute of Technology, Banaras Hindu University, Varanasi–221005, India
3. Department of Mathematics, Banaras Hindu University, Varanasi–221005, India
4. Department of Mathematics, University of Allahabad, Allahabad, India