The group of homomorphisms of Abelian torsion groups.
The homological dimension of a torsion-free abelian group of finite rank as a module over its ring of endomorphisms
The pseudorational rank of an Abelian group.
The theory of dual groups
We study the -theory of sequences of dual groups and give a complete classification of the -elementary classes by finding simple invariants for them. We show that nonstandard models exist.