2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/78002Paper withdrawn. There is a gap in the proof of Proposition 4.3 (its conclusion ``d'où la proposition.'' is incorrect). Therefore theorems 1.1 and 3.1, which were the main results of the paper, are not proved.29 pages, Plain TeXAlgebraic Geometrytext