Affiliation: | 1.Department of Mathematics,Hong Kong Baptist University,Kowloon, Hong Kong,China;2.Computer Science Department,Stanford University,Stanford,USA;3.Departamento de Matemática Aplicada e Estátistica,ICMC-S?o Carlos-USP,S?o Carlos,Brazil;4.Departamento de Matemática – UFPR,Centro Politécnico,Curitiba,Brazil |