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北美退伍军人节(Veterans Day),12 日无更新
arXiv 2007.12478math.GR
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一个有限生成 profinite 群的虚拟生成图

The virtually generating graph of a profinite group

Andrea Lucchini

AI总结:

研究有限生成 profinite 群的虚拟生成图,证明移除孤立顶点后的图连通分支数可任意指定,且另一相关子图连通且直径至多 3。

摘要:

我们考虑图 $\Gamma_{\rm{virt}}(G)$,其顶点是有限生成 profinite 群 $G$ 的元素,两个顶点 $x$ 和 $y$ 相邻当且仅当它们拓扑生成 $G$ 的一个开子群。我们研究从 $\Gamma_{\rm{virt}}(G)$ 中移除孤立顶点后得到的图 $\Delta_{\rm{virt}}(G)$ 的连通性。特别地,我们证明对于每个正整数 $t$,存在一个有限生成 prosoluble 群 $G$,使得 $\Delta_{\rm{virt}}(G)$ 恰好有 $t$ 个连通分支。此外,我们研究图 $\tilde \Gamma_{\rm{virt}}(G)$,其顶点同样是 $G$ 的元素,两个顶点相邻当且仅当存在 $G$ 的一个最小生成集包含它们。在这种情况下,我们证明移除孤立顶点后得到的子图 $\tilde \Delta_{\rm{virt}}(G)$ 是连通的,且直径至多为 3。

英文摘要:

We consider the graph $Γ_{\rm{virt}}(G)$ whose vertices are the elements of a finitely generated profinite group $G$ and where two vertices $x$ and $y$ are adjacent if and only if they topologically generate an open subgroup of $G$. We investigate the connectivity of the graph $Δ_{\rm{virt}}(G)$ obtained from $Γ_{\rm{virt}}(G)$ by removing its isolated vertices. In particular we prove that for every positive integer $t$, there exists a finitely generated prosoluble group $G$ with the property that $Δ_{\rm{virt}}(G)$ has precisely $t$ connected components. Moreover we study the graph $\tilde Γ_{\rm{virt}}(G)$, whose vertices are again the elements of $G$ and where two vertices are adjacent if and only if there exists a minimal generating set of $G$ containing them. In this case we prove that the subgraph $\tilde Δ_{\rm{virt}}(G)$ obtained removing the isolated vertices is connected and has diameter at most 3.

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