• Characterisation of Relations Admitting Left Kan Lifts Along Them. The following conditions are equivalent:
    1. The left Kan lift
      \[ \text{Lift}_{R}\colon \mathbf{Rel}\webleft (X,B\webright )\to \mathbf{Rel}\webleft (X,A\webright ) \]

      along $R$ exists.

    2. The relation $R$ admits a right adjoint in $\textbf{Rel}$.
    3. The relation $R$ is of the form $\text{Gr}\webleft (f\webright )$ (as in Definition 7.3.1.1.1) for some function $f$.

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