Help understanding Mac Lane exercise (2.4.1) ch. II, sec. 1, ex. 1, p.41 – math.stackexchange.com
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This is the problem in question from Mac Lane's "Categories for the Working Mathematician", chapter 2, section 4, exercise 1:
For $R$ a ring, describe $R\mbox{-}\mathbf{Mod}$ as a full ...