Torsion-free Abelian groups of rank 3

Torsion-free Abelian groups similar in properties to torsion-free Abelian groups of rank 3, in particular the groups of rank 3 themselves, can be characterized up to quasi-isomorphism by means of certain invariants. From the invariants of each such group one can compute invariants of its pure subgroups and invariants of its factor-groups modulo its pure subgroups.
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