2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/69746The first part of this paper, written mainly for nonspecialists, is a short and partial survey about the construction and classification of nilpotent Cohen-Macaulay scheme structures on a scheme "less nilpotent"(e.g. a smooth variety) as support. The second part presents some old and new examples about degree 4 curves in the projective space and inexistence of certain vector bundles.16 pages. This sketch of a survey will appear in the Proceedings of the German-Romanian Seminar, Cluj-Napoca, September 2003Algebraic Geometry14-02;13-02; 14H10text