Equidivisibility and profinite coproduct

Abstract

The aim of this work is to investigate the behavior of equidivisibility under coproduct in the category of pro-$\mathsf{V}$ semigroups, where $\mathsf{V}$ is a pseudovariety of finite semigroups. Exploring the relationship with the two-sided Karnofsky--Rhodes expansion, the notions of KR-cover and strong KR-cover for profinite semigroups are introduced. The former is stronger than equidivisibility and the latter provides a characterization of equidivisible profinite semigroups with an extra mild condition, so-called letter super-cancellativity. Furthermore, under the assumption that $\mathsf{V}$ is closed under two-sided Karnofsky--Rhodes expansion, closure of some classes of equidivisible pro-$\mathsf{V}$ semigroups under(finite) $\mathsf{V}$-coproduct is established.