I am studying Algebraic Topology, homology and cohomology to be concrete. I am reading\working through Hatcher, Rotman, Harper and sometimes I combine them with other books when none of them give a satisfactory answer to my questions.
Why Rotman, Hatcher, and most of the books I look at use free abelian groups when defining singular (co)chains instead of using free modules over an arbitrary commutative ring with multiplicative identity?
Harper is the only one I know that does it with modules.
Hope the question is not off-topic. I just feel I am missing something.