1. Systems Research Institute, Polish Academy of Sciences , ul. Newelska 6, 01-447 Warszawa , Poland
2. School of Mathematical Sciences , East China Normal University , Shanghai , China
3. InstitutÉlie Cartan de Lorraine, UMR 7502 , Université de Lorraine , B.P. 70239, 54506 Vandoeuvre-lès-Nancy Cedex , France