2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/174516We develop a new method leading the structure of finite subsets S and T of an abelian group with $|S+T|\le |S|+|T|$. We show also how to recover the known results in this area in a relatively short space.29 pagesNumber Theory11B60; 11B34; 20D60text