A Coalgebraic Semantics for Intuitionistic Modal Logic
Rodrigo Nicolau Almeida, Nick Bezhanishvili
TL;DR
The paper addresses the problem of providing a coalgebraic semantics for intuitionistic modal logic with $\Box$, focusing on descriptive intuitionistic modal frames and image-finite Kripke frames. It introduces the $V_{G}$ and $V^{\uparrow}$ constructions and proves equivalences: $\mathbf{CoAlg}(V_{G}(V^{\uparrow}(-))) \simeq \mathbf{DiG}$ and $\mathbf{CoAlg}(P_{G}(\mathsf{Up}(-))) \simeq \mathbf{ImFinK}$, thereby enabling a modular coalgebraic treatment of intuitionistic frames. The paper also provides a bisimulation correspondence, a dual description of the free modal Heyting algebra on finitely many generators, and a pathway to coalgebraic intuitionistic logic via neighbourhood-style semantics. Together, these results create a framework for extending coalgebraic methods to intuitionistic logics and suggest avenues for handling logics such as $\mathsf{S4}$ in a coalgebraic setting.
Abstract
We give a new coalgebraic semantics for intuitionistic modal logic with $\Box$. In particular, we provide a colagebraic representation of intuitionistic descriptive modal frames and of intuitonistic modal Kripke frames based on image-finite posets. This gives a solution to a problem in the area of coalgebaic logic for these classes of frames, raised explicitly by Litak (2014) and de Groot and Pattinson (2020). Our key technical tool is a recent generalization of a construction by Ghilardi, in the form of a right adjoint to the inclusion of the category of Esakia spaces in the category of Priestley spaces. As an application of these results, we study bisimulations of intuitionistic modal frames, describe dual spaces of free modal Heyting algebras, and provide a path towards a theory of coalgebraic intuitionistic logics.
