The monoidal unit of $\mathsf{Rel}$ is the functor

\[ \mathbb {1}^{\mathsf{Rel}}\colon \text{pt}\to \mathsf{Rel} \]

picking the set

\[ \mathbb {1}_{\mathsf{Rel}}\mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}\text{pt} \]

of $\mathsf{Rel}$.


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