The monoids in $\boldsymbol {\mathsf{Rel}}$ with respect to the Cartesian monoidal structure of Proposition 8.3.3.8.1 are called hypermonoids, and their theory is explored in 
. Similarly, the comonoids in $\boldsymbol {\mathsf{Rel}}$ are called hypercomonoids, and they are defined and studied in .
8.4.6 Co/Monoids
