Normal Forms for Elements of ${}^*$-Continuous Kleene Algebras Representing the Context-Free Languages

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Main Authors: Hopkins, Mark, Leiß, Hans
Format: Preprint
Published: 2023
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author Hopkins, Mark
Leiß, Hans
author_facet Hopkins, Mark
Leiß, Hans
contents Within the tensor product $K \mathop{\otimes_{\cal R}} C_2'$ of any ${}^*$-continuous Kleene algebra $K$ with the polycyclic ${}^*$-continuous Kleene algebra $C_2'$ over two bracket pairs there is a copy of the fixed-point closure of $K$: the centralizer of $C_2'$ in $K \mathop{\otimes_{\cal R}} C_2'$. Using an automata-theoretic representation of elements of $K\mathop{\otimes_{\cal R}} C_2'$ à la Kleene, with the aid of normal form theorems that restrict the occurrences of brackets on paths through the automata, we develop a foundation for a calculus of context-free expressions without variable binders. We also give some results on the bra-ket ${}^*$-continuous Kleene algebra $C_2$, motivate the ``completeness equation'' that distinguishes $C_2$ from $C_2'$, and show that $C_2'$ already validates a relativized form of this equation.
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id arxiv_https___arxiv_org_abs_2310_17295
institution arXiv
publishDate 2023
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spellingShingle Normal Forms for Elements of ${}^*$-Continuous Kleene Algebras Representing the Context-Free Languages
Hopkins, Mark
Leiß, Hans
Formal Languages and Automata Theory
F.4.3
Within the tensor product $K \mathop{\otimes_{\cal R}} C_2'$ of any ${}^*$-continuous Kleene algebra $K$ with the polycyclic ${}^*$-continuous Kleene algebra $C_2'$ over two bracket pairs there is a copy of the fixed-point closure of $K$: the centralizer of $C_2'$ in $K \mathop{\otimes_{\cal R}} C_2'$. Using an automata-theoretic representation of elements of $K\mathop{\otimes_{\cal R}} C_2'$ à la Kleene, with the aid of normal form theorems that restrict the occurrences of brackets on paths through the automata, we develop a foundation for a calculus of context-free expressions without variable binders. We also give some results on the bra-ket ${}^*$-continuous Kleene algebra $C_2$, motivate the ``completeness equation'' that distinguishes $C_2$ from $C_2'$, and show that $C_2'$ already validates a relativized form of this equation.
title Normal Forms for Elements of ${}^*$-Continuous Kleene Algebras Representing the Context-Free Languages
topic Formal Languages and Automata Theory
F.4.3
url https://arxiv.org/abs/2310.17295