[1] Univ Mazandaran, Fac Math Sci, Dept Math, Babol Sar, Iran
[2] Istanbul Univ, Fac Sci, Dept Math, TR-34134 Istanbul, Turkey
[3] Tshwane Univ Technol, Fac Sci, Dept Math & Stat, ZA-0001 Pretoria, South Africa
[4] North West Univ, Int Inst Symmetry Anal & Math Modelling, Dept Math Sci, ZA-2735 Mmabatho, South Africa