1. Department of Mathematics, Maharaja Agrasen University, Baddi, Solan, HP, India;
2. School of Basic Sciences (Mathematics), Bahra University, Waknaghat, Solan, HP, India;
3. Department of Mathematics, PRS Govt. College Baijnath, Kangra, HP, India;
4. Department of Applied Mathematics, University of Calcutta, Kolkata, India