2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/31003The Expansion property considered by researchers in Social Choice is shown to correspond to a logical property of nonmonotonic consequence relations that is the {\em pure}, i.e., not involving connectives, version of a previously known weak rationality condition. The assumption that the union of two definable sets of models is definable is needed for the soundness part of the result.9 pages. UnpublishedArtificial IntelligenceI.2.3text