• Associativity. Given a diagram

    in $\mathsf{Sets}_{*}$, we have isomorphisms of pointed sets

    \[ \webleft (X\times _{W}Y\webright )\times _{V}Z\cong \webleft (X\times _{W}Y\webright )\times _{Y}\webleft (Y\times _{V}Z\webright ) \cong X\times _{W}\webleft (Y\times _{V}Z\webright ), \]

    where these pullbacks are built as in the diagrams


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