Affiliation: | 1. Faculty of Mathematics, University “Al.I. Cuza”, Ia?i 700506, Romania;2. Institute of Mathematics “Octav Mayer”, Ia?i 700506, Romania;3. UMR CNRS 5466 MAB and INRIA Futurs Anubis, case 26, Université Victor Segalen Bordeaux 2, 33076 Bordeaux Cedex, France |