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arXiv · 2105.08815

A point-free approach to canonical extensions of boolean algebras and bounded archimedean $\ell$-algebras

G. Bezhanishvili·L. Carai·P. Morandi
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Abstract

In \cite{BH20} an elegant choice-free construction of a canonical extension of a boolean algebra $B$ was given as the boolean algebra of regular open subsets of the Alexandroff topology on the poset of proper filters of $B$. We make this construction point-free by replacing the Alexandroff space of proper filters of $B$ with the free frame $\mathcal{L}$ generated by the bounded meet-semilattice of all filters of $B$ (ordered by reverse inclusion) and prove that the booleanization of $\mathcal{L}$ is a canonical extension of $B$. Our main result generalizes this approach to the category $\boldsymbol{\mathit{ba}\ell}$ of bounded archimedean $\ell$-algebras, thus yielding a point-free construction of canonical extensions in $\boldsymbol{\mathit{ba}\ell}$. We conclude by showing that the algebra of normal functions on the Alexandroff space of proper archimedean $\ell$-ideals of $A$ is a canonical extension of $A\in\boldsymbol{\mathit{ba}\ell}$, thus providing a generalization of the result of \cite{BH20} to $\boldsymbol{\mathit{ba}\ell}$.

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G. Bezhanishvili, L. Carai, P. Morandi. 2021-05-18. A point-free approach to canonical extensions of boolean algebras and bounded archimedean $\ell$-algebras. https://arxiv.org/abs/2105.08815

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