\begin{notn} Let $ \mathbf{A} $ and $ \mathscr{S} $ be categories. For each $ A \in \mathbf{A} $ , there is a functor $ \begin{array}{cccc} \ev_A{\colon}\linebreak[0] &\ftrcat{\mathbf{A}}{\mathscr{S}} & \to &\mathscr{S} \ &X & \mapsto &X(A), \end{array} $ called evaluation at $ A $ . We will be working with diagrams in $ \ftrcat{\mathbf{A}}{\mathscr{S}} $ , and given such a diagram $ D{\colon}\linebreak[0] \mathbf{I} \to \ftrcat{\mathbf{A}}{\mathscr{S}} $ , we have for each $ A \in \mathbf{A} $ a functor $ \begin{array}{cccc} \ev_A \circ D{\colon}\linebreak[0]&\mathbf{I} &\to &\mathscr{S} \ &I &\mapsto &D(I)(A). \end{array} $ We write $ \ev_A \circ D $ as $ D( - )(A) $ .