Constructive completeness and non-discrete languages

TL;DR

This paper unifies and extends constructive completeness results using categorical logic and sheaf semantics, connecting various semantics and enabling completeness theorems for complex and non-discrete languages.

Contribution

It provides a conceptual framework linking constructive completeness with multiple semantics, including new theorems for non-discrete languages and arbitrary sizes.

Findings

Unified categorical framework for constructive completeness

New completeness theorems for non-discrete languages

Connections between Tarski, presheaf, sheaf, Kripke, and Beth semantics

Abstract

We give an analysis and generalizations of some long-established constructive completeness results in terms of categorical logic and pre-sheaf and sheaf semantics. The purpose is in no small part conceptual and organizational: from a few basic ingredients arises a more unified picture connecting constructive completeness with respect to Tarski semantics, to the extent that it is available, with various completeness theorems in terms of presheaf and sheaf semantics (and thus with Kripke and Beth semantics). From this picture are obtained both ("reverse mathematical") equivalence results and new constructive completeness theorems; in particular, the basic set-up is flexible enough to obtain strong constructive completeness results for languages of arbitrary size and languages for which equality between the elements of the signature is not decidable.