Institution: | (1) Henri Poincaré-Nancy 1, Institut Élie Cartan, Université, BP 239, 54506 Vanduvre Cedex, France;(2) Department of Algebra and Number Theory, Eötvös Loránd University, H-1518 Budapest, Pf. 120, 1117, Budapest, Pázmány Péter Sétány 1/C, Hungary |