Gabriel Agnew | Searcharxiv

arXiv2026

On Local Finiteness of Modal K4 Algebras

We study local finiteness for modal $K4$ algebras via the tunability of their dual general frames. In particular, we provide a sufficient condition for modal $K4$ algebras to be locally finite by identifying a structure which must be present in non-locally finite modal $K4$ algebras. We then show that this condition becomes both necessary and sufficient for complex modal $K4$ algebras. Next, we translate this condition into a pair of order-theoretic conditions on transitive Kripke frames, providing a classification of local finiteness on their dual modal algebras. We further show that the logic of any class of well-founded transitive relations with no infinite antichains has the finite model property, and conclude that the logic of the class of well-quasi orderings has the finite model property.

math.LO↗

arXiv2025

On distance logics of Euclidean spaces

We consider logics derived from Euclidean spaces $\mathbb{R}^n$. Each Euclidean space carries relations consisting of those pairs that are, respectively, distance more than 1 apart, distance less than 1 apart, and distance 1 apart. Each relation gives a uni-modal logic of $\mathbb{R}^n$ called the farness, nearness, and constant distance logics, respectively. These modalities are expressive enough to capture various aspects of the geometry of $\mathbb{R}^n$ related to bodies of constant width and packing problems. This allows us to show that the farness logics of the spaces $\mathbb{R}^n$ are all distinct, as are the nearness logics, and the constant distance logics. The farness and nearness logics of $\mathbb{R}$ are shown to strictly contain those of $\mathbb{Q}$, while their constant distance logics agree. It is shown that the farness logic of the reals is not finitely axiomatizable and does not have the finite model property.

math.LO↗