A Lindstrom characterisation of the guarded fragment and of modal logic with a global modality 1
Martin Otto, Robert Piro · 2008
abstract. We establish a Lindström type characterisation of the exten-sion of basic modal logic by a global modality (ML[∀]) and of the guarded fragment of first-order logic (GF) as maximal among compact logics with the corresponding bisimulation invariance and the Tarski Union Property.