2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/73780The result in theorem 2.1 has been strengthened (see theorem 2.3) and the remarks in the introduction and the text adapted to this new result. Also some misprints in the previous version have been corrected.13 pagesNumber TheoryRepresentation Theory11F70; 22E50text