Definition 35.4.9. Let R be a ring. Define the contravariant functor C : \text{Mod}_ R \to \text{Mod}_ R by setting
C(M) = \mathop{\mathrm{Hom}}\nolimits _{\textit{Ab}}(M, \mathbf{Q}/\mathbf{Z}),
with the R-action on C(M) given by rf(s) = f(rs).
Comments (0)
There are also: