Self-small mixed abelian groups G with G/T(G) finite rank divisible

We investigate the class G of self-small mixed abelian groups G with G/T(G) finite rank divisible and the category QG with objects groups in G and maps quasi-homomorphisms. We employ several existing dualities and equivalences between subcategories of QG and subcategories of the category of locally-free torsion-free finite rank abelian groups and quasi-homomorphisms as well as a new duality in QG and new category equivalences from subcategories of QG to certain rational algebras. To aid in our investigations, we also introduce a new invariant and several notions of type for mixed groups. Our results mostly involve classification of subclasses of G in terms of more well-known objects. In particular, we obtain more or less satisfactory descriptions for rank two groups in G, groups in G analogous to cohesive torsion-free groups and groups in G analogous to Murley groups, underlining the resemblance between the mixed groups in G and locally free torsion-free groups of finite rank. For example, we show that ev...