> **Puzzles 159.** The categories I've been calling \$$\mathcal{C}\$$ and \$$\mathcal{D}\$$ have other, more purely mathematical names. More precisely, they are _isomorphic_ to two other categories we've already seen in this course, which have more mathematical names. What are those other categories?

I think \$$\mathcal{C}\$$ has been called "\$$\mathbf{2}\$$" in other discussions and \$$\mathcal{D}\$$ has been called "\$$\mathbf{1}\$$".