[1] Pavanatma Coll, Dept Math, Murickassery, India
[2] Univ Ljubljana, Fac Math & Phys, Ljubljana, Slovenia
[3] Inst Math Phys & Mech, Ljubljana, Slovenia
[4] Univ Maribor, Fac Nat Sci & Math, Maribor, Slovenia
[5] Univ Cadiz, Dept Estadist & Invest Operat, Algeciras, Spain
[6] St Pauls Coll Kalamassery, Dept Math, Kochi, India
[7] Cochin Univ Sci & Technol, Dept Math, Kochi, India