1. Department of Mathematics, The University of Burdwan, Burdwan 713104, West Bengal, India
2. Department of Mathematics, Institute of Science, Banaras Hindu University, Varanasi 221005, Uttar Pradesh India
3. Department of Mathematics, Babeş-Bolyai University, Cluj-Napoca 400084, Romania
4. Department of Mathematics, Institute of Science, Banaras Hindu University, Varanasi 221005, Uttar Pradesh, India