1. Ph.D. Candidate, Dept. of Mathematics, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India.
2. Associate Professor, Dept. of Mathematics, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001, India (corresponding author).
3. Retired; formerly, Professor of Mathematics, Dept. of Mathematics, Indian Institute of Science, Bangalore, Karnataka 560012, India.