By the way: Proposition 2.20 in the book says that any symmetric monoidal preorder \\(\mathcal{V}\\) has an opposite \\(\mathcal{V}^{\text{op}}\\); completing the proof of this result is [Exercise 2.21](https://forum.azimuthproject.org/discussion/1983/exercise-21-chapter-2/p1), and then in [Exercise 2.22](https://forum.azimuthproject.org/discussion/1984/exercise-22-chapter-2/p1) you're invited to study \\(\mathbf{Cost}^{\text{op}}\\). Everyone should give them a try!