Section 1: Definition of ring Exercise 1.13 Section 5: Modules over a ring Notes Exercise 5.14 Exercise 5.15 Exercise 5.16 Exercise 5.17 Exercise 5.18 Section 6: Products, coproducts, etc., in R-ModR\operatorname{-}{\rm Mod}R-Mod Notes Exercise 6.1 Exercise 6.2 Exercise 6.3 Exercise 6.4 Exercise 6.5 Exercise 6.6 Exercise 6.7 Exercise 6.8 Exercise 6.9 Exercise 6.10 Exercise 6.11 Exercise 6.12 Exercise 6.13 Exercise 6.14 Exercise 6.15 Exercise 6.16