[1] Univ Ljubljana, Ljubljana, Slovenia
[2] Inst Math Phys & Mech, Ljubljana, Slovenia
[3] Univ Pannonia, Veszprem, Hungary
[4] Czech Acad Sci, Inst Comp Sci, Vodarenskou vezi 2, Prague 18207, Czech Republic
[5] Cent China Normal Univ, Sch Math & Stat, Wuhan, Peoples R China
[6] Cent China Normal Univ, Hubei Key Lab Math Sci, Wuhan, Peoples R China
[7] Cent European Univ, Budapest, Hungary
[8] Univ Pannonia, Dept Comp Sci & Syst Technol, Veszprem, Hungary
[9] HUN REN Alfred Reny Inst Math, Budapest, Hungary
[10] Shandong Univ, Sch Math, Jinan, Peoples R China