A comprehensive combination framework

Abstract

We define a general notion of a fragment within higher-order type theory; a procedure for constraint satisfiability in combined fragments is outlined, following Nelson-Oppen schema. The procedure is in general only sound, but it becomes terminating and complete when the shared fragment enjoys suitable noetherianity conditions and admits an abstract version of a “Keisler-Shelah-like” isomorphism theorem. We show that this general decidability transfer result covers recent work on combination in first-order theories as well as in various intensional logics such as description, modal, and temporal logics.