Internal structures in the category of right-preordered groups

Abstract

We give explicit axioms for the algebraic theory of the quasivarieties of right-preordered groups and preordered groups. We then look at lattices of effective equivalence relations, which turn out to be similar to the lattices of equivalence relations in the category of groups. Once this is established, we study internal structures in the category of right-preordered groups. We start with some general results and then prove the S-protomodularity of the category of right-preordered groups, when considering the class S of Schreier split epimorphisms. Following this, we investigate further and prove that the category of right-preordered groups turns out to be action representable when we restrict our attention to split epimorphisms in S. Relatively to this class of split epimorphisms, we define the notion of S-precrossed modules, and then of S-crossed modules; that correspond exactly to Schreier internal reflexive graphs and Schreier internal categories, respectively. Lastly, we characterize groupoids among Schreier internal categories and give some examples.