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arXiv 1608.02572math.GR
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Thompson群$F$的生成问题

The generation problem in Thompson group $F$

Gili Golan

摘要:

我们证明了Thompson群$F$中的生成问题是可判定的,即,存在一种算法,其决定$F$的元素的有限集是否生成整个$F$。该算法利用了$F$的子群的Stallings $2$ -核,其可以以类似的方式定义为一个随机生成的自由群的子群的Stallings核。对$F$子群的Stallings $2$ -核的进一步研究,为解决$F$中的另一个算法问题提供了一种方法.也就是说,给定$F$的一个非线性生成子群$H$,如果$H$传递地作用在有限并元分式集$\mathcal D$上,则它是可判定的。研究的其他应用包括构造$F$的新的无穷指数极大子群,其中,一个无穷指数极大子群传递作用于集合$\mathcal D$,以及构造$F$的初等顺从子群,它在$F$的正规子群中是极大的.

英文摘要:

We show that the generation problem in Thompson group $F$ is decidable, i.e., there is an algorithm which decides if a finite set of elements of $F$ generates the whole $F$. The algorithm makes use of the Stallings $2$-core of subgroups of $F$, which can be defined in an analogue way to the Stallings core of subgroups of a finitely generated free group. Further study of the Stallings $2$-core of subgroups of $F$ provides a solution to another algorithmic problem in $F$. Namely, given a finitely generated subgroup $H$ of $F$, it is decidable if $H$ acts transitively on the set of finite dyadic fractions $\mathcal D$. Other applications of the study include the construction of new maximal subgroups of $F$ of infinite index, among which, a maximal subgroup of infinite index which acts transitively on the set $\mathcal D$ and the construction of an elementary amenable subgroup of $F$ which is maximal in a normal subgroup of $F$.

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