论文标题

免费组的有限近似I:$ f $ inverse封面问题

Finite approximation of free groups I: the $F$-inverse cover problem

论文作者

Auinger, K., Bitterlich, J., Otto, M.

论文摘要

对于有限连接的图形$ \ MATHCAL {e} $,带有一组边缘$ e $,构建了有限的$ e $ e $ e $ G $ $ g $,使得$ g $满足的关系集$ p = 1 $(在$ e \ e \ cup e \ cup e \ cup e^{-1} $)上封闭了生成器的封闭。结果,g $中的每个元素$ g \都承认了一个唯一的最小值$ \ mathrm {c}(g)边缘的$($ g $ of $ g $)代表$ g $作为$ g $作为$ \ mathrm {c}(c}(c}(g)(g)\ cup \ cup \ mathrm {c} c} c} c}(g)(g)(g)(g)( The crucial property of the group $G$ is that connectivity in the graph $\mathcal{E}$ is encoded in $G$ in the following sense: if a word $p$ forms a path $u\longrightarrow v$ in $\mathcal{E}$ then there exists a $G$-equivalent word $q$ which also forms a path $u\longrightarrow v$ and uses only edges from their content;特别是,相应组元素$ [p] _g = [q] _g $的内容跨越了一个连接的子图,该子图的$ \ mathcal {e} $包含vertices $ u $和$ v $。由于$ e $生成的免费组显然具有这些属性,因此构造提供了另一个实例,说明了如何在有限组中``近似''或``模拟''的某些特征。作为应用程序,显示每个有限的副互动都允许有限的$ f $ inverse盖。这解决了Henckell和Rhodes的长期问题。

For a finite connected graph $\mathcal{E}$ with set of edges $E$, a finite $E$-generated group $G$ is constructed such that the set of relations $p=1$ satisfied by $G$ (with $p$ a word over $E\cup E^{-1}$) is closed under deletion of generators (i.e.~edges). As a consequence, every element $g\in G$ admits a unique minimal set $\mathrm{C}(g)$ of edges (the \emph{content} of $g$) needed to represent $g$ as a word over $\mathrm{C}(g)\cup\mathrm{C}(g)^{-1}$. The crucial property of the group $G$ is that connectivity in the graph $\mathcal{E}$ is encoded in $G$ in the following sense: if a word $p$ forms a path $u\longrightarrow v$ in $\mathcal{E}$ then there exists a $G$-equivalent word $q$ which also forms a path $u\longrightarrow v$ and uses only edges from their content; in particular, the content of the corresponding group element $[p]_G=[q]_G$ spans a connected subgraph of $\mathcal{E}$ containing the vertices $u$ and $v$. As the free group generated by $E$ obviously has these properties, the construction provides another instance of how certain features of free groups can be ``approximated'' or ``simulated'' in finite groups. As an application it is shown that every finite inverse monoid admits a finite $F$-inverse cover. This solves a long-standing problem of Henckell and Rhodes.

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