Anyone know a decent reference on the basic theory of direct limits of groups, from an elementary (meaning group theoretic, as opposed to categorical) perspective? Finitely generated abelian groups are pretty much the only object of relevance for me, though general abelian groups (esp. Prufer groups and $\mathbb{Q}$) might crop up later on.
The books I have on group theory and algebra just don't cover it, or it's only covered very briefly. Is there a decent reference that lays out the basics? How it commutes with iteration and products (direct, sum, free, tensor), torsion/rank, Aut(G), ext/tor/hom, divisibility, fixed points of actions, what happens when the limit stabilizes, or the group is constant, or all the maps are epis/monos, representations, etc. That sort of stuff. Especially, when (if not always) can it be written as a limit of some proper subsequence of the $G_\alpha$'s? And in that case, when is it a nice sort of resolution?
Is anyone aware of a good reference for this from the group-theoretic viewpoint? Obviously the fgag case probably has module-theoretic treatments in some homological algebra textbook (though again, not in the ones I have), but I'd still prefer it from the perspective of groups.
If someone wants to drop a bunch of the basic facts requested above (with at least partial proofs, tho no heavy category talk) I'll hit you with a 500 bounty, but a reference would still be really nice!