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Motivation and Details:

Thinking back a couple of years ago, when I did combinatorial group theory a lot, I decided to explore the idea that whenever an element of a group has finite order $n$, then there exist elements in that group of orders each power of $n$.

This lead me to the following definition of mine:

Definition: Let $G$ be a group. If for all $n\in\Bbb N$, if $g\in G$ with $|g|=n$ we have for all $m\in\Bbb N$ there is at least one $h_m\in G$ with $|h_m|=n^m$, call $G$ powerful-element.

These groups exist:

Example: Consider $G=\Bbb Z$ or $$G=\prod_{m=1}^\infty \Bbb Z_{p^m}$$ for prime $p$.

The Question:

Let $G$ be a powerful-element group that is not torsionfree${}^\dagger$. Can $G$ be finitely presented?

Thoughts:

Of course, $G$ is infinite.

I thought for a while that I had found a finitely generated, powerful element group that is not torsion free. Here is the candidate:

Let $p$ be prime. Consider the group $G$ given by the presentation

[. . .]

$$Q=\langle a,b\mid a^p, \{(b^mab^{-m})^{p^m}\mid m\in\Bbb N\}\rangle.$$

But that didn't work: see this question of mine.

So I'm stuck.

My guess is that, no, no such group exists, but I wouldn't be surprised if one did; so I'm really hedging my bets on this one.

Context:

This is the sort of problem I think I could answer myself, provided luck and a few months' time. Like I said: I did a lot of combinatorial group theory during a PhD attempt (that turned into an MPhil for a number of reasons); but now I'm doing a postgraduate research degree in linear algebraic groups and I don't have enough time.

The kind of answer I'm looking for is an complete solution. This could be asking too much, though, given the nature of how some problems in the area are easy to state but exceptionally difficult to solve.

Please help :)


$\dagger$: That is, there does exist a torsion element: an $x\in G$ of finite order.

Shaun
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    Have you heard of Higman's embedding theorem? If not, you should read about it. – Moishe Kohan Jun 09 '23 at 23:48
  • I just did. It's interesting, @MoisheKohanonstrike. Thank you. I don't see how it helps though. – Shaun Jun 10 '23 at 00:41
  • Then think for another hour or so. – Moishe Kohan Jun 10 '23 at 01:25
  • Just in case: you should use the existence of a universal f.p. group containing all f.p. groups as subgroups (up to an isomorphism). – Moishe Kohan Jun 10 '23 at 01:34
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    @MoisheKohanonstrike but you still need to show the existence of group which is finitely generated and recursive enumerable relation which is also a power element group (as defined in question) – Balaji sb Jun 10 '23 at 01:42
  • @Balajisb: nope. – Moishe Kohan Jun 10 '23 at 01:45
  • countably generated and power element group exits with finite set of relations: $G = {e^{j 2 \pi r}: r \ is \ a \ rational \ number | e^{j 2 \pi} = 1 , e^{j0} = 1}$. This group is countable and the number of relations is only two and element of every integer order exits. – Balaji sb Jun 10 '23 at 01:48
  • @MoisheKohanonstrike I see. Good one. Is it possible to explicitly give a group ? – Balaji sb Jun 10 '23 at 01:57
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    @Balajisb: Valiev, M. K. Universal group with twenty-one defining relations. Discrete Math. 17 (1977), no. 2, 207–213. – Moishe Kohan Jun 10 '23 at 02:34
  • @MoisheKohanonstrike Thanks ! Quite an interesting result. – Balaji sb Jun 10 '23 at 02:44

1 Answers1

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Look at first paragraph of Universal Finitely Presented Group

It's enough to provide a countably generated, recursively presented powerful-element group.

One such group is $$G = \{e^{j 2 \pi r}: r \in \mathbb{Q} \mid e^{j 2 \pi} = 1, e^{j0} = 1\}.$$

Shaun
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Balaji sb
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