• Adjointness. We have an adjunction
    witnessed by a bijections of sets
    \[ \textup{Hom}_{\mathcal{P}\webleft (A\webright )}\webleft (R_{*}\webleft (U\webright ),V\webright )\cong \textup{Hom}_{\mathcal{P}\webleft (A\webright )}\webleft (U,R_{-1}\webleft (V\webright )\webright ), \]

    natural in $U\in \mathcal{P}\webleft (A\webright )$ and $V\in \mathcal{P}\webleft (B\webright )$, i.e. such that:

    • The following conditions are equivalent:
      • We have $R_{*}\webleft (U\webright )\subset V$.
      • We have $U\subset R_{-1}\webleft (V\webright )$.


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