2-Adjointness. We have an adjunction witnessed by an isomorphism of categories
\[ \mathsf{Fun}\webleft (\mathcal{G},\mathcal{D}\webright )\cong \mathsf{Fun}\webleft (\mathcal{G},\mathsf{Core}\webleft (\mathcal{D}\webright )\webright ), \]
natural in $\mathcal{G}\in \text{Obj}\webleft (\mathsf{Grpd}\webright )$ and $\mathcal{D}\in \text{Obj}\webleft (\mathsf{Cats}\webright )$, forming, together with the 2-functor $\mathrm{K}_{0}$ of Item 2 of Proposition 9.4.3.1.3, a triple 2-adjunction
witnessed by isomorphisms of categories
\begin{align*} \mathsf{Fun}\webleft (\mathrm{K}_{0}\webleft (\mathcal{C}\webright ),\mathcal{G}\webright ) & \cong \mathsf{Fun}\webleft (\mathcal{C},\mathcal{G}\webright ),\\ \mathsf{Fun}\webleft (\mathcal{G},\mathcal{D}\webright ) & \cong \mathsf{Fun}\webleft (\mathcal{G},\mathsf{Core}\webleft (\mathcal{D}\webright )\webright ),\end{align*}
natural in $\mathcal{C},\mathcal{D}\in \text{Obj}\webleft (\mathsf{Cats}\webright )$ and $\mathcal{G}\in \text{Obj}\webleft (\mathsf{Grpd}\webright )$.