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arXiv · 2504.16663

Online and feasible presentability: from trees to modal algebras

Nikolay Bazhenov·Dariusz Kalociński·Michał Wrocławski
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Abstract

We investigate whether every computable member of a given class of structures admits a fully primitive recursive (also known as punctual) or fully P-TIME copy. A class with this property is referred to as punctually robust or P-TIME robust, respectively. We present both positive and negative results for structures corresponding to well-known representations of trees, such as binary trees, ordered trees, sequential (or prefix) trees, and partially ordered (poset) trees. A corollary of one of our results on trees is that semilattices and lattices are not punctually robust. In the main result of the paper, we demonstrate that, unlike Boolean algebras, modal algebras - that is, Boolean algebras with modality - are not punctually robust. The question of whether distributive lattices are punctually robust remains open. The paper contributes to a decades-old program on effective and feasible algebra, which has recently gained momentum due to rapid developments in punctual structure theory and its connections to online presentations of structures.

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Nikolay Bazhenov, Dariusz Kalociński, Michał Wrocławski. 2025-04-23. Online and feasible presentability: from trees to modal algebras. https://arxiv.org/abs/2504.16663

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