Finitely Generated Abelian Groups [HB 25]

Changes:

• The function AllHomomorphisms for abelian groups has been renamed to Homomorphisms.

New features:

• The function Centralizer(H, K) for abelian groups H and K is now allowed, provided only that H and K have a common supergroup. (Previously K had to be a subgroup of H.)
• The function DirectSum has been added to take a sequence of abelian groups, and to return the direct sum, with the appropriate maps.