Characterising modal definability of team-based logics via the universal modality (Q2273015)

Universal modality is the genuine Leibnizian notion of modality, especially universal necessity. This idea implies truth always, in all possible situations, independent and free of any kind of accessibility relation. This clear and precise paper deals with a modal logic in which any occurrence of a universal modality is positive. For this fragment, a result relating definability with ways to build models and frames in modal logic is proved (i.e Goldblatt-Thomason theorem). Moreover, this subsystem is also considered and studied in the realm of team semantics.