Institution: | Département de Mathématiques, Laboratoire C.N.R.S. U.M.R. 6205, Université de Bretagne Occidentale, 6, Avenue Victor Le Gorgeu, CS 93837, 29238 Brest Cedex 3, France ; Faculty of Mathematics, ``Al.I. Cuza" University of Iasi, Bd. Carol I, no. 11, 700506 Iasi, Romania |