2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/78550It is proved that a smooth rational surface in projective four-space, which is ruled by cubics or quartics has degree at most 12. It is also proved that a smooth rational surface in projective four-space which is the image of Fn by a linear system with "simple base points" (see text) has degree at most 12.PlainTex; to appearAlgebraic Geometry14J26text