Hybrid languages
Settling that the modal language is one of the means describing relational structures, the authors enrich it by operators explicitly ``speaking'' about some properties of these structures. Expressive relations of the obtained languages become clear. It is proved that logics of the subtended semantics of the languages are undecidable and make it possible ``to feel'' finiteness of a model.
scientific article; zbMATH DE number 856769
scientific article