Topologies on groups determined by sets of convergent sequences

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.