7

For various types of groups, there exist catalogues of those groups of the particular type which are "small" in a certain sense. — For example:

and so on.

Question: Does there exist such data library for groups with "short" finite presentations?

Remarks:

  • There is a 12-years-old question asking for such database. At that time, apparently such database was not available. But maybe this has changed in the meantime(?)

  • When setting the length of a finite presentation equal to the sum of the lengths of the relators, for every presentation on two generators of length at most $10$, it is straightforward to decide whether the corresponding group $G$ is trivial, nontrivial but finite, or infinite (if $G$ is infinite, this can be seen from the abelian invariants of $G$, $G'$ or $G''$, and if $G$ is finite, coset enumeration finishes even with very small limits). Where things start to get more interesting is length $11$. One of the few examples for which deciding finiteness seems more tricky is the group $$ G \ := \ \langle a, b \ | \ a^3 = ab^{-3}a^{-1}b^{-1}a^{-1}b = 1 \rangle. $$ What is easy to see is that $G/G'' \cong {\rm C}_{37} \rtimes {\rm C}_9$, and that $G''$ is perfect — but beyond that, things seem to get more difficult. Almost for sure, people have considered this presentation (and other similar presentations) before. Looking into an appropriate data library would tell what is known about that (and other similar) groups immediately.

Glasby
  • 1,961
Stefan Kohl
  • 19,498
  • 21
  • 73
  • 136
  • 4
    Giles Gardam’s thesis contains a useful census of all one-relator groups with relator length less than 9 or so (up to Nielsen equivalence). – Carl-Fredrik Nyberg Brodda May 29 '22 at 11:53
  • 3
    Marco Linton maintains a database of one-relator presentations here: https://warwick.ac.uk/fac/sci/maths/people/staff/linton/homepage/ . – HJRW May 29 '22 at 12:13
  • 1
    In writing such tables It would be useful to have rules so as to add $c(x,y)=xy^{-1}$ and $[x,y]=xyx^{-1}y^{-1}$ in the language and thus consider, say, $[x,[x,y]]$ as a very short relator (of length maybe 3 rather than 10). – YCor Jun 30 '22 at 11:23

1 Answers1

3

I would very much like to have such a database and would like to contribute to its development. Prompted by this question, we talked about what such a database could look like (e.g. in terms of groups covered, functionality etc.) at a discussion session of a workshop in Manchester with Ian Leary, Marco Linton, Saul Schleimer and Henry Wilton. I encourage anyone interested in this to contact me.

As some inspiration, I'll link this mathoverflow question on atlas-like websites.

Giles Gardam
  • 2,861