1. Department of Mathematics, R. M. K. College of Engineering and Technology, Puduvoyal 601206, India
2. Gofa Camp, Near Gofa Industrial College and German Adebabay, Nifas Silk-Lafto, Addis Ababa 26649, Ethiopia
3. Institute of Mathematical Sciences, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia
4. Department of Mathematics, Loyola College, Chennai 600034, India