[Song, Ying-Qing] Hunan City Univ, Coll Sci, Yiyang 413000, Peoples R China.
[Hamid, Aamir] Quaid i Azam Univ, Dept Math, Islamabad 44000, Pakistan.
[Khan, M. Ijaz] Riphah Int Univ, Dept Math & Stat, Islamabad 44000, Pakistan.
[Prasannakumara, B. C.; Kumar, R. Naveen; Gowda, R. J. Punith] Davangere Univ, Dept Studies & Res Math, Davangere, Karnataka, India.
[Khan, Sami Ullah] COMSATS Islamabad, Dept Math, Sahiwal 57000, Pakistan.