A $1$-morphism $f\colon A\to B$ of $\mathcal{C}$ is corepresentably fully faithful1 if the following equivalent conditions are satisfied:
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1.
The $1$-morphism $f$ is corepresentably full (Definition 13.2.2.1.1) and corepresentably faithful (Definition 13.2.1.1.1).
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2.
For each $X\in \operatorname {\mathrm{Obj}}\webleft (\mathcal{C}\webright )$, the functor
\[ f^{*}\colon \mathsf{Hom}_{\mathcal{C}}\webleft (B,X\webright )\to \mathsf{Hom}_{\mathcal{C}}\webleft (A,X\webright ) \]given by precomposition by $f$ is fully faithful.
- 1Further Terminology: Corepresentably fully faithful morphisms have also been called lax epimorphisms in the literature (e.g. in [AESV, On Functors Which Are Lax Epimorphisms]), though we will always use the name “corepresentably fully faithful morphism” instead in this work.