8.7.9 Functors Corepresentably Fully Faithful on Cores

Let $\mathcal{C}$ and $\mathcal{D}$ be categories.

A functor $F\colon \mathcal{C}\to \mathcal{D}$ is corepresentably fully faithful on cores if, for each $X\in \text{Obj}\webleft (\mathsf{Cats}\webright )$, the postcomposition by $F$ functor

\[ F_{*}\colon \mathsf{Core}\webleft (\mathsf{Fun}\webleft (\mathcal{X},\mathcal{C}\webright )\webright )\to \mathsf{Core}\webleft (\mathsf{Fun}\webleft (\mathcal{X},\mathcal{D}\webright )\webright ) \]

is fully faithful.

In detail, a functor $F\colon \mathcal{C}\to \mathcal{D}$ is corepresentably fully faithful on cores if it satisfies the conditions in Remark 8.7.7.1.2 and Remark 8.7.8.1.2, i.e.:

  1. For all diagrams of the form

    if $\alpha $ and $\beta $ are natural isomorphisms and we have

    \[ \alpha \mathbin {\star }\text{id}_{F}=\beta \mathbin {\star }\text{id}_{F}, \]

    then $\alpha =\beta $.

  2. For each $\mathcal{X}\in \text{Obj}\webleft (\mathsf{Cats}\webright )$ and each natural isomorphism
    there exists a natural isomorphism
    such that we have an equality
    of pasting diagrams in $\mathsf{Cats}_{\mathsf{2}}$, i.e. such that we have
    \[ \beta =\alpha \mathbin {\star }\text{id}_{F}. \]

Is there a characterisation of functors corepresentably fully faithful on cores?


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