[1] Univ Sci & Technol China, Sch Math Sci, Hefei 230026, Anhui, Peoples R China
[2] East China Normal Univ, Sch Math Sci, Shanghai Key Lab PMMP, Shanghai 200241, Peoples R China
[3] Henan Univ, Sch Math & Stat, Kaifeng 475004, Henan, Peoples R China