• Corepresentably Full Morphisms in $\textbf{Rel}$. The following conditions are equivalent:
    1. The morphism $R\colon A\mathrel {\rightarrow \kern -9.5pt\mathrlap {|}\kern 6pt}B$ is a corepresentably full morphism.
    2. For each pair of relations $S,T\colon X\mathrel {\rightrightarrows \kern -9.5pt\mathrlap {|}\kern 6pt}A$, the following condition is satisfied:
      • If $S\mathbin {\diamond }R\subset T\mathbin {\diamond }R$, then $S\subset T$.
    3. The functor
      \[ R^{-1}\colon \webleft (\mathcal{P}\webleft (B\webright ),\subset \webright )\to \webleft (\mathcal{P}\webleft (A\webright ),\subset \webright ) \]

      is full.

    4. For each $U,V\in \mathcal{P}\webleft (B\webright )$, if $R^{-1}\webleft (U\webright )\subset R^{-1}\webleft (V\webright )$, then $U\subset V$.
    5. The functor
      \[ R_{-1}\colon \webleft (\mathcal{P}\webleft (B\webright ),\subset \webright )\to \webleft (\mathcal{P}\webleft (A\webright ),\subset \webright ) \]

      is full.

    6. For each $U,V\in \mathcal{P}\webleft (B\webright )$, if $R_{-1}\webleft (U\webright )\subset R_{-1}\webleft (V\webright )$, then $U\subset V$.

Noticed something off, or have any comments? Feel free to reach out!


You can also use the contact form below: