[Fan, Aihua; Fan, Shilei] Cent China Normal Univ, Sch Math & Stat, Wuhan 430079, Hubei, Peoples R China.
[Fan, Aihua] Univ Picardie, CNRS, UMR 7352, LAMFA, 33 Rue St Leu, Amiens, France.
[Fan, Shilei] Cent China Normal Univ, Hubei Key Lab Math Sci, Wuhan 430079, Hubei, Peoples R China.
[Qiu, Yanqi] Chinese Acad Sci, AMSS, Inst Math, Beijing 100190, Peoples R China.
[Qiu, Yanqi] Chinese Acad Sci, AMSS, Hua Loo Keng Key Lab Math, Beijing 100190, Peoples R China.