1. Université de Lyon, Université Lyon 1, CNRS UMR 5208 Institut Camille Jordan, 43, boulevard du 11 novembre 1918, F-69622 Villeurbanne Cedex, France
2. Simion Stoilow Institute of Mathematics of the Romanian Academy, Calea Griviţei 21, 010702 Bucureşti, Romania
3. Department of Mathematics, Rutgers University, Hill Center, Busch Campus, 110 Frelinghuysen Rd., Piscataway, NJ 08854, USA
4. Mathematics Department, Technion - Israel Institute of Technology, Haifa, 32000, Israel