Go Hashimoto

Daniel Găină, Go Hashimoto

In this paper, we establish an analogue of Craig Interpolation Property for a many-sorted variant of first-order hybrid logic. We develop a forcing technique that dynamically adds new constants to the underlying signature in a way that preserves consistency, even in the presence of models with possibly empty domains. Using this forcing method, we derive general criteria that are sufficient for a signature square to satisfy Craig interpolation property.

Go Hashimoto

Variables are a crucial element in logic and are also addressed in institution theory, an effort to axiomatize logic. In institution theory, we typically use extensions (signature morphisms) obtained from variables instead of introducing variables directly. While this approach appears simple at first glance because it does not introduce new structures, it often requires numerous conditions to describe variable structures, which can actually complicate the discussion. In this paper, we propose introducing variable structures directly by utilizing a generalization of category of functors. We define a category of predicate logics and formulate the introduction of compound sentences as a functor. We also introduce a proof system and prove a completeness theorem.

Go Hashimoto

Transition Algebra (TA) is a type of infinite logic introduced to discuss rewriting systems. The natural deductive proof systems already introduced in TA satisfy completeness for countable signatures. However, it lacks compactness, making it unsuitable for practical applications. This time, we will create a compact proof system by restricting the (Star) rule to induction. We will also use a sequent proof system instead of natural deduction. Furthermore, we will introduce a semantics that makes this system complete, and its application (a model-theoretic proof of Craig interpolation).