[1] Marywood Univ, Dept Math & Comp Sci, Scranton, PA 18509 USA
[2] Florida Int Univ, Dept Math, Miami, FL 33199 USA
[3] Henan Polytech Univ, Sch Math & Informat Sci, Jiaozuo 454000, Henan, Peoples R China
[4] Oklahoma State Univ, Dept Math, Stillwater, OK 74078 USA
[5] Beijing Normal Univ, Sch Math Sci, Beijing 100875, Peoples R China
[6] Beijing Normal Univ, Lab Math & Complex Syst, Minist Educ, Beijing 100875, Peoples R China