Thompson's group $F$ is almost $\frac{3}{2}$-generated

TL;DR

The paper shows that Thompson's group F is nearly 3/2-generated, meaning most elements can be extended to generating pairs, and explores subgroup properties related to its derived subgroup and finite index subgroups.

Contribution

It introduces the concept of 'almost' 3/2-generation for Thompson's group F and establishes new subgroup generation results related to its derived subgroup.

Findings

Every element with abelianization part of a generating pair in Z^2 is part of a generating pair in F.

For each non-trivial element, there exists a g such that ⟨f,g⟩ contains the derived subgroup of F.

If f is outside the derived subgroup, ⟨f,g⟩ can have finite index in F.

Abstract

Recall that a group $G$ is said to be $\frac{3}{2}$-generated if every non-trivial element of $G$ belongs to a generating pair of $G$. Thompson's group $V$ was proved to be $\frac{3}{2}$-generated by Donoven and Harper in 2019. It was the first example of an infinite finitely presented non-cyclic $\frac{3}{2}$-generated group. Recently, Bleak, Harper and Skipper proved that Thompson's group $T$ is also $\frac{3}{2}$-generated. In this paper, we prove that Thompson's group $F$ is "almost" $\frac{3}{2}$-generated in the sense that every element of $F$ whose image in the abelianization forms part of a generating pair of $\mathbb{Z}^2$ is part of a generating pair of $F$. We also prove that for every non-trivial element $f\in F$ there is an element $g\in F$ such that the subgroup $\langle f,g\rangle$ contains the derived subgroup of $F$. Moreover, if $f$ does not belong to the derived subgroup of $F$, then there is an element $g\in F$ such that $\langle f,g\rangle$ has finite index in $F$.