[1] Univ Lorraine, CNRS, IECL, F-54000 Nancy, France
[2] Univ Aix Marseille, Inst Univ France, Inst Math Marseille, CNRS UMR 7373, 163, Ave Luminy, Case 907, F-13288 Marseille 9, France
[3] Graz Univ Technol, Inst Anal & Number Theory, A-8010 Graz, Austria