• Monoidality. The diagonal map
    \[ \Delta \colon \text{id}_{\mathsf{Sets}}\Longrightarrow \mathord {\times }\circ {\Delta ^{\mathsf{Cats}_{\mathsf{2}}}_{\mathsf{Sets}}}, \]

    is a monoidal natural transformation:

    1. Compatibility With Strong Monoidality Constraints. For each $X,Y\in \text{Obj}\webleft (\mathsf{Sets}\webright )$, the diagram

      commutes.

    2. Compatibility With Strong Unitality Constraints. The diagrams
      commute, i.e. we have
      \begin{align*} \Delta _{\text{pt}} & = \lambda ^{\mathsf{Sets},-1}_{\text{pt}}\\ & = \rho ^{\mathsf{Sets},-1}_{\text{pt}}, \end{align*}

      where we recall that the equalities

      \begin{align*} \lambda ^{\mathsf{Sets}}_{\text{pt}} & = \rho ^{\mathsf{Sets}}_{\text{pt}},\\ \lambda ^{\mathsf{Sets},-1}_{\text{pt}} & = \rho ^{\mathsf{Sets},-1}_{\text{pt}}\end{align*}

      are always true in any monoidal category by , of .


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