2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/225702We prove that a certain Brill-Noether locus over a non-hyperelliptic curve $C$ of genus 4, is isomorphic to the \textit{Donagi-Izadi cubic threefold} in the case when the pencils of the two trigonal line bundles of $C$ coincide.8 pages, sort of appendix to the article [arxiv:0810.4392], any comments welcomeAlgebraic Geometry14D20, 14E05text