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arXiv 2002.10278math.GRmath.LOmath.RA
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双曲群中的增长率

The rates of growth in a hyperbolic group

Koji Fujiwara, Zlil Sela

AI总结:

本文研究双曲群及其子群、子半群在所有有限生成集下的增长率集合,证明这些集合良序并确定极限群情形的序数为 $ω^ω$。

摘要:

我们研究一个双曲群关于其所有有限生成集的增长率所构成的可数集合。我们证明该集合是良序的,并且在群的自同构意义下,每个实数至多可以是有限多个生成集的增长率。我们证明增长率集合的序数至少为 $ω^ω$;而当该群是极限群时(例如自由群和曲面群),该序数恰为 $ω^ω$。我们进一步研究一个双曲群的所有有限生成子群关于其所有有限生成集的增长率。该集合同样被证明是良序的,并且对于给定的双曲群,每个实数至多可以是其子群的有限生成集的有限多个同构类的增长率。最后,我们将结果加强到包含一个双曲群的所有子半群的所有有限生成集的增长率。

英文摘要:

We study the countable set of rates of growth of a hyperbolic group with respect to all its finite generating sets. We prove that the set is well-ordered, and that every real number can be the rate of growth of at most finitely many generating sets up to automorphism of the group. We prove that the ordinal of the set of rates of growth is at least $ω^ω$, and in case the group is a limit group (e.g., free and surface groups), it is $ω^ω$. We further study the rates of growth of all the finitely generated subgroups of a hyperbolic group with respect to all their finite generating sets. This set is proved to be well-ordered as well, and every real number can be the rate of growth of at most finitely many isomorphism classes of finite generating sets of subgroups of a given hyperbolic group. Finally, we strengthen our results to include rates of growth of all the finite generating sets of all the subsemigroups of a hyperbolic group.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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