• Interaction With Postcomposition. The following conditions are equivalent:
    1. The functor $F\colon \mathcal{C}\to \mathcal{D}$ is faithful.
    2. For each $\mathcal{X}\in \text{Obj}\webleft (\mathsf{Cats}\webright )$, the postcomposition functor
      \[ F_{*} \colon \mathsf{Fun}\webleft (\mathcal{X},\mathcal{C}\webright ) \to \mathsf{Fun}\webleft (\mathcal{X},\mathcal{D}\webright ) \]

      is faithful.

    3. The functor $F\colon \mathcal{C}\to \mathcal{D}$ is a representably faithful morphism in $\mathsf{Cats}_{\mathsf{2}}$ in the sense of Chapter 11: Types of Morphisms in Bicategories, Definition 11.1.1.1.1.

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