[1] Quaid I Azam Univ 45320, Dept Math, Islamabad 45320, Pakistan
[2] King Abdulaziz Univ, Fac Sci, Dept Math, Nonlinear Anal & Appl Math NAAM Res Grp, POB 80257, Jeddah 21589, Saudi Arabia
[3] Heriot Watt Univ, Edinburgh Campus, Edinburgh EH14 4AS, Midlothian, Scotland