Varieties of modal algebras without the congruence extension property

Zalán Gyenis; Zalán Molnár

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arXiv · 2402.07293

Varieties of modal algebras without the congruence extension property

Zalán Gyenis·Zalán Molnár

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Abstract

In a recent paper, Krawczyk proved that there are continuum many axiomatic extensions of global consequence associated with the modal system $E$ that do not admit the local deduction detachment theorem. In algebraic parlance, he showed that there are continuum many varieties of modal algebras lacking the congruence extension property. In this paper, we extend Krawczyk's results and construct a continuum of varieties of modal algebras that do not have the congruence extension property, but that do admit other, logically relevant properties, such as monotonicity, extensiveness, idempotency, normality, etc. This gives a continuum of axiomatic extensions of the corresponding modal systems not having the local deduction detachment theorem.

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BibTeX RIS

Zalán Gyenis, Zalán Molnár. 2024-02-11. Varieties of modal algebras without the congruence extension property. https://arxiv.org/abs/2402.07293

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