[Fan, Shilei] Cent China Normal Univ, Hubei Key Lab Math Sci, Sch Math & Stat, Wuhan 430079, Hubei, Peoples R China.
[Fan, Shilei] Aix Marseille Univ, Inst Math Marseille, CNRS, Cent Marseille,UMR7373, 39 Rue F Joliot Curie, F-13453 Marseille, France.
[Liao, Lingmin] Univ Paris Est Creteil Val de Marne, CNRS, UMR 8050, LAMA, 61 Ave Gen de Gaulle, F-94010 Creteil, France.