两种上下文无关语言交集的剖析能力

Josef Rukavicka
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引用次数: 1

摘要

我们说一门语言$L$是\emph{不断发展}的,如果有一个常数$c$,使得每个单词$u\in L$后面都有一个单词$v\in L$和$\vert u\vert<\vert v\vert\leq c+\vert u\vert$。如果存在一个常数$c$,使得对于每个单词$u\in L$都有一个单词$v\in L$与$\vert u\vert<\vert v\vert\leq c\vert u\vert$对应,我们就说一种语言$L$\emph{呈几何级数增长}。给定两种无限语言$L_1,L_2$,我们说$L_1$将$L_2$\emph{分解}为$\vert L_2\setminus L_1\vert=\infty$和$\vert L_1\cap L_2\vert=\infty$。2013年,研究表明,对于每一种不断发展的语言$L$,都有一种常规的语言$R$, $R$可以分解$L$。在本文中,我们将展示如何通过两种无关上下文的语言的交集的同态象来解剖几何增长的语言。考虑三个字母$\Gamma$、$\Sigma$和$\Theta$,即$\vert \Sigma\vert=1$和$\vert \Theta\vert=4$。我们证明存在与环境无关的语言$M_1,M_2\subseteq \Theta^*$、可擦除的字母同态$\pi:\Theta^*\rightarrow \Sigma^*$和不可擦除的字母同态$\varphi : \Gamma^*\rightarrow \Sigma^*$,从而:如果$L\subseteq \Gamma^*$是一个几何增长的语言,那么存在一个正则语言$R\subseteq \Theta^*$,使得$\varphi^{-1}\left(\pi\left(R\cap M_1\cap M_2\right)\right)$解析语言$L$。
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Dissecting power of intersection of two context-free languages
We say that a language $L$ is \emph{constantly growing} if there is a constant $c$ such that for every word $u\in L$ there is a word $v\in L$ with $\vert u\vert<\vert v\vert\leq c+\vert u\vert$. We say that a language $L$ is \emph{geometrically growing} if there is a constant $c$ such that for every word $u\in L$ there is a word $v\in L$ with $\vert u\vert<\vert v\vert\leq c\vert u\vert$. Given two infinite languages $L_1,L_2$, we say that $L_1$ \emph{dissects} $L_2$ if $\vert L_2\setminus L_1\vert=\infty$ and $\vert L_1\cap L_2\vert=\infty$. In 2013, it was shown that for every constantly growing language $L$ there is a regular language $R$ such that $R$ dissects $L$. In the current article we show how to dissect a geometrically growing language by a homomorphic image of intersection of two context-free languages. Consider three alphabets $\Gamma$, $\Sigma$, and $\Theta$ such that $\vert \Sigma\vert=1$ and $\vert \Theta\vert=4$. We prove that there are context-free languages $M_1,M_2\subseteq \Theta^*$, an erasing alphabetical homomorphism $\pi:\Theta^*\rightarrow \Sigma^*$, and a nonerasing alphabetical homomorphism $\varphi : \Gamma^*\rightarrow \Sigma^*$ such that: If $L\subseteq \Gamma^*$ is a geometrically growing language then there is a regular language $R\subseteq \Theta^*$ such that $\varphi^{-1}\left(\pi\left(R\cap M_1\cap M_2\right)\right)$ dissects the language $L$.
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来源期刊
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14.30%
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期刊介绍: DMTCS is a open access scientic journal that is online since 1998. We are member of the Free Journal Network. Sections of DMTCS Analysis of Algorithms Automata, Logic and Semantics Combinatorics Discrete Algorithms Distributed Computing and Networking Graph Theory.
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