1. Department of Mathematics, Institute of Science, Banaras Hindu University, Varanasi, India shyam_lal@rediffmail.com
2. Department of Mathematics, Institute of Science, Banaras Hindu University, Varanasi, India vivek.jaimatadi.sharma7@gmail.com
3. Department of Mathematics, Institute of Science, Banaras Hindu University, Varanasi, India patelnehabhu@gmail.com