Groups that are the union of two semigroups have left-orderable quotients

Abstract

In this article, we show that a group $G$ is the union of two proper subsemigroups if and only if $G$ has a nontrivial left-orderable quotient. Furthermore, if $G$ is the union of two proper semigroups, then there exists a minimum normal subgroup $N⊴G$ for which $G/N$ is left-orderable and nontrivial.

7 pages