For simplicity, I will ignore size issues in this question.
Let $\mathcal{D}$ and $\mathcal{O}$ denote categories. By a function $\mathcal{D} \rightarrow \mathcal{O},$ let us mean a functor from the core of $\mathcal{D}$ into the core of $\mathcal{O}$. Now let $\mathcal{C}$ and $\mathcal{D}$ denote categories, and suppose we're given a faithful functor $U : \mathcal{C} \rightarrow \mathcal{D}$. Then we get a function $p : \mathcal{D} \rightarrow \mathbf{Ord}$ as follows. (By $\mathbf{Ord}$, I mean the category of preordered sets).
Fix $D,D' \in \mathbf{D}$. Then:
- As a set, define $p(D) = \{(X,i) \mid X \in \mathrm{Obj}(\mathbf{C}),\; i : \mathrm{Iso}(UX,D)\}.$
- $(X,i) \leq (Y,j)$ in $p(D)$ iff there exists a morphism $f : X \rightarrow Y$ with $i = j \circ Uf$.
- Given an isomorphism $f : D \rightarrow D',$ define $p(f)$ to be the mapping $(X,i) \in D \mapsto (X,f \circ i) \in D'.$
Examples.
Let $\mathcal{D}$ denote the category of sets, and consider a set $D$.
If $\mathcal{C}$ is the category of graphs, then $p(D)$ is equivalent to the poset of all graphs with underlying set $D$, ordered in the usual way.
If $\mathcal{C}$ is the category of topological spaces, then $p(D)$ is equivalent to the poset of all topologies on $D$, ordered in reverse to the usual way.
Questions.
- Does this construction have a name?
- Where can I learn more?