2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/60099The revised version has two additional references and a shorter proof of Proposition 5.7. This version also makes numerous small changes and has an appendix containing a proof of the degree formula for a parametrized surface.24 pages. LaTeX2e with amsmath and amsfonts packagesAlgebraic GeometryCommutative Algebra14Q10 (Primary) 13D02, 14Q05, 65D17 (Secondary)text