• Interaction With Groupoids. If $\mathcal{C}$ and $\mathcal{D}$ are groupoids, then the following conditions are equivalent:
    1. The functor $F$ is an equivalence of groupoids.
    2. The following conditions are satisfied:
      1. The functor $F$ induces a bijection
        \[ \pi _{0}\webleft (F\webright )\colon \pi _{0}\webleft (\mathcal{C}\webright )\to \pi _{0}\webleft (\mathcal{D}\webright ) \]

        of sets.

      2. For each $A\in \text{Obj}\webleft (\mathcal{C}\webright )$, the induced map
        \[ F_{x,x}\colon \mathrm{Aut}_{\mathcal{C}}\webleft (A\webright )\to \mathrm{Aut}_{\mathcal{D}}\webleft (F_{A}\webright ) \]

        is an isomorphism of groups.


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