Interval orders, semiorders and ordered groups

Abstract

We prove that the order of an ordered group is an interval order if and only if it is a semiorder. Next, we prove that every semiorder is isomorphic to a collection J of intervals of some totally ordered abelian group, these intervals being of the form [x,x+α[ for some positive α. We describe ordered groups such that the ordering is a semiorder and we introduce threshold groups generalizing totally ordered groups. We show that the free group on finitely many generators and the Thompson group F can be equipped with a compatible semiorder which is not a weak order. On another hand, a group introduced by Clifford cannot.