Topologies on groups determined by sets of convergent sequences

TL;DR

This paper characterizes $s$-groups, a class of Hausdorff topological groups defined by convergence of sequences, showing they are quotients of Graev free topological groups over metrizable or sequential spaces.

Contribution

It provides a new characterization of $s$-groups as quotients of Graev free topological groups over specific spaces, linking sequence convergence with free topological group structures.

Findings

$s$-groups include all sequential Hausdorff groups

Quotients of Graev free topological groups are exactly the non-discrete $s$-groups

The characterization applies to Abelian $s$-groups as well

Abstract

A Hausdorff topological group $(G,\tau)$ is called an $s$-group and $\tau$ is called an $s$-topology if there is a set $S$ of sequences in $G$ such that $\tau$ is the finest Hausdorff group topology on $G$ in which every sequence of $S$ converges to the unit. The class $\mathbf{S}$ of all $s$-groups contains all sequential Hausdorff groups and it is finitely multiplicative. A quotient group of an $s$-group is an $s$-group. For a non-discrete topological group $(G,\tau)$ the following three assertions are equivalent: 1) $(G,\tau)$ is an $s$-group, 2) $(G,\tau)$ is a quotient group of a Graev free topological group over a metrizable space, 3) $(G,\tau)$ is a quotient group of a Graev free topological group over a sequential Tychonoff space. The Abelian version of this characterization of $s$-groups holds as well.