[1] Univ Grenoble Alpes, Inst Fourier, Dept Math, UMR 5582, CS40700, F-38058 Grenoble 9, France
[2] Univ Vienna, Dept Math, Nordbergstr 15, Vienna, Austria
[3] Moscow MV Lomonosov State Univ, Inst Theoret & Expt Phys, Mech Math Dept, Kharkevich Inst Informat Transmiss Problems, Moscow, Russia