[1] Univ Paris Diderot, Sorbonne Paris Cite, CNRS, PPS, Paris, France
[2] Univ Paris Sud, LRI, Orsay, France
[3] Chinese Acad Sci, Inst Software, State Key Lab Comp Sci, Beijing, Peoples R China
[4] Univ Lorraine, LORIA, Nancy, France
[5] Univ Turin, Dipartimento Informat, I-10149 Turin, Italy