Enriched concepts of regular logic

Abstract

Building on our previous work on enriched universal algebra, we define a notion of enriched language consisting of function and relation symbols whose arities are objects of the base of enrichment. In this context, we construct atomic formulas and define the regular fragment of enriched logic by taking conjunctions and existential quantifications of those. We then characterize enriched categories of models of regular theories as enriched injectivity classes in the enriched category of structures. These notions rely on the choice of a factorization system on the base of enrichment which will be used to interpret relation symbols and existential quantifications.