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Algebra Universalis
Article . 2017 . Peer-reviewed
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Article . 2017
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Congruence kernels in Ockham algebras

Authors: Blyth, T. S.; Silva, H. J.;

Congruence kernels in Ockham algebras

Abstract

For an Ockham algebra \((\mathcal{L}; f)\), the authors consider the ideals \(I\) such that \(I=0/\upsilon\) for some congruence \(\upsilon\) on \((\mathcal{L}; f)\). These ideals are called \textit{congruence kernels} and the congruence \(\upsilon\) for which \(I=0/\upsilon\) is said to have kernel \(I\). The set \(\mathcal{I}_K(\mathcal{L})\) of congruence kernels of \(\mathcal{L}\) ordered by set inclusion is a complete lattice. The authors introduce the set \(\mathcal{I}_2(\mathcal{L}):=\{I\in \mathcal{\mathcal{I}}(L): f^{2}(I)\subseteq I\}\), \(\mathcal{I}(\mathcal{L})\) being the set of ideals of \(\mathcal{L}\). It happens that \(\mathcal{I}_2(\mathcal{L})\) is a complete sub-lattice of \(\mathcal{I}(\mathcal{L})\) and \(\mathcal{I}_K(\mathcal{L})\subseteq \mathcal{I}_2(\mathcal{L})\). For a given ideal \(I\in \mathcal{I}(\mathcal{L})\), the authors define \(\tilde{I}:=\{x\in L: x\wedge f(i)\in I \text{ for some } i\in I\}\) in order to show that \(I\in \mathcal{I}_K(\mathcal{L})\) iff \(f^{2}(I)\subseteq I\) and \(I= \tilde{I}\). For \(I\in \mathcal{I}_K(\mathcal{L})\), the authors show that the smallest congruence with kernel \(I\), call it \(\varphi (I)\), is defined by \[ (x,y)\in \varphi (I) \text{ iff } (\exists i\in I) \text{ such that } (x\vee i)\wedge f(i)= (y\vee i)\wedge f(i). \] To give a description of the largest congruence having a given kernel \(I\in \mathcal{I}_K(\mathcal{L})\), the authors define for each \(a\in L\) and each \(n\in \mathbb{N}\) the set \(W_{a,n}^{I}:= \{x\in L: f^{n}(a)\wedge x\in I\}\) and the binary relation \(\Theta_{n}^{I}:=\{(a,b) : W_{a,n}^{I}=W_{b,n}^{I}\}\) and show that \(\Theta^{I}:=\bigcap_{n\in \mathbb{N}}\Theta_{n}^{I}\) is the largest congruence on \(\mathcal{L}\) having kernel \(I\). The authors give the following characterization of the proper congruence kernels in terms of the prime ideals of \(\mathcal{L}\): \[ L\neq I\in \mathcal{I}_K(\mathcal{L}) \text{ iff } I=\bigcap\{P\in \mathcal{I}_p(\mathcal{L}): I\subseteq P, P\cap f(I)=\emptyset, f^{2}(I)\subseteq P\}. \] \(I_p(L)\) is the set of prime ideals of \(\mathcal{L}\). For a subset \(X\) of \(L\), let \(\kappa (X)\) be the smallest congruence kernel containing \(X\). Write \(\kappa (a)\) when \(X=\{a\}\). The authors show that \(\mathcal{I}_K(\mathcal{L})\) is modular iff for all \(a,b,c\in L\), \(\kappa (a\vee c)\cap \kappa (a\vee b) \subseteq \kappa((\kappa (a\vee c)\cap \kappa (b))\cup \kappa (c))\) and \(\mathcal{I}_K(\mathcal{L})\) is distributive iff for all \(a,b,c\in L\), \(\kappa (a)\cap \kappa (b\vee c)\subseteq \kappa((\kappa(a)\cap \kappa(b))\cup (\kappa(a)\cap \kappa(c)))\).

Keywords

De Morgan algebras, Łukasiewicz algebras (lattice-theoretic aspects), Lattice ideals, congruence relations, Structure and representation theory of distributive lattices, congruence, Ockham algebra, kernel ideal, congruence kernels

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
2
Average
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