Definition:Domain Functor

Definition
Let $\mathbf C$ be a metacategory.

Let $\mathbf C^\to$ be its morphism category.

The domain functor is the functor $\operatorname{\mathbf{dom}}: \mathbf C^\to \to \mathbf C$ defined by:

That it is in fact a functor is shown on Domain Functor is Functor.

The functor $\mathbf{dom}$ can be represented as follows:


 * $\begin{xy}

<0em,2em>*+{A} = "A", <0em,-2em>*+{B} = "B", <4em,2em>*+{A'} = "A2", <4em,-2em>*+{B'} = "B2",

"A";"B" **@{-} ?>*@{>} ?*!/^1em/{f}, "A";"A2" **@{-} ?>*@{>} ?*!/_1em/{g_1}, "A2";"B2" **@{-} ?>*@{>} ?*!/_1em/{f'}, "B";"B2" **@{-} ?>*@{>} ?*!/^1em/{g_2},

<6em,0em>;<10em,0em> **@{~} ?>*@2{>} ?*!/_1em/{\mathbf{dom}},

<12em,2em>*+{A} = "AA", <16em,2em>*+{A'} = "AA2",

"AA";"AA2" **@{-} ?>*@{>} ?*!/_1em/{g_1}, \end{xy}$

It is thus seen to be an example of a forgetful functor.