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arXiv · 1908.01659

Varieties of positive modal algebras and structural completeness

T. Moraschini
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Abstract

Positive modal algebras are the positive-subreducts of modal algebras. We prove that the variety of positive S4-algebras is not locally finite. On the other hand, the free one-generated positive S4-algebra is shown to be finite. Moreover, we describe the bottom part of the lattice of varieties of positive S4-algebras. Building on this, we characterize (passively, hereditarily) structurally complete varieties of positive K4-algebras.

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T. Moraschini. 2019-08-01. Varieties of positive modal algebras and structural completeness. https://arxiv.org/abs/1908.01659

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