The binary quasiorder on semigroups

Abstract

Given two elements $x,y$ of a semigroup $X$ we write $x\lesssim y$ if for every homomorphism $\chi :X\to \{0,1\}$ we have $\chi (x)\le \chi (y)$. The quasiorder $\lesssim$ is called the $binary$ $quasiorder$ on $X$. It induces the equivalence relation $\Updownarrow$ that coincides with the least semilattice congruence on $X$. In the paper we discuss some known and new properties of the binary quasiorder on semigroups.

9 pages (this is the first part of the previous paper, which has been split into two parts)