1. Department of Mathematics, Bangabasi Evening College, 19 Rajkumar Chakraborty Sarani, Kolkata 700009, West Bengal, India
2. Department of Pure Mathematics, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700019, West Bengal, India
3. Department of Mathematics, Bankim Sardar College, Tangrakhali, Taldi, South 24 Parganas 743329, West Bengal, India