2020-12-21
group theory – The direct sum $\oplus$ versus the cartesian product $\times$

The Question : 129 people think this question is useful In the case of abelian groups, I have been treating these two set operations as more or less indistinguishable. In early mathematics courses, one normally defines $A^n := A\times A\times\ldots\times A$; however in, for example, the fundamental theorem of finitely generated abelian groups, we normally