The linear bicategory of relations is the linear bicategory consisting of:
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The Underlying Bicategory I. The bicategory $\mathsf{Rel}$ of Definition 8.3.4.1.1.
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The Underlying Bicategory II. The bicategory $\mathsf{Rel}$ of Definition 8.4.2.1.1.
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Linear Distributors. The inclusions
\begin{align*} \delta ^{\ell }_{R,S,T} & \colon T\mathbin {\diamond }(S\mathbin {\square }R) \hookrightarrow (T\mathbin {\diamond }S)\mathbin {\square }R,\\ \delta ^{r}_{R,S,T} & \colon (T\mathbin {\square }S)\mathbin {\diamond }R \hookrightarrow T\mathbin {\square }(S\mathbin {\diamond }R) \end{align*}of Item 5 of Proposition 8.1.4.1.3.
