a bimodule taking values in the category \cattwo = \{\bot \lt \top\} = \{0 \lt 1\},
i.e., a functor \leftcat(\graphsoverx\leftcat{)\op} \times \rightcat(\setsunderx\rightcat) \buildrel \textstyle\forktwoone \over {\class{fork}\rightarrow} \cattwo
The kernel K and quotient Q functors provide representations of the \forktwoone bimodule:
\begin{array}{}
\leftcat(\graphsoverx\leftcat{)\op} \mathrel{\leftcat\times} \leftcat(\graphsoverx\leftcat) & \xleftarrow{\textstyle \leftcat 1_\graphsoverx \times \rightadj K} &
\leftcat(\graphsoverx\leftcat{)\op} \times \rightcat(\setsunderx\rightcat) & \xrightarrow{\textstyle \leftadj{Q\op} \times \rightcat 1_\setsunderx} &
\rightcat(\setsunderx\rightcat{)\op} \mathrel{\rightcat\times} \rightcat(\setsunderx\rightcat)\\
\llap{\hom {\mathrel-} {\leftcat(\graphsoverx\leftcat)} \sim} \leftcat{\Bigg\downarrow} & \cong & \class{fork}{\Bigg\downarrow}\rlap\forktwoone & \cong & \rightcat{\Bigg\downarrow} \rlap{\hom {\mathrel-} {\rightcat(\setsunderx\rightcat)} \sim}\\
\Set & \xleftarrow{} & \cattwo & \xrightarrow{} & \Set\\
\end{array}
Each of the two bottom arrows in the above diagram is the functor which takesthe arrow \bot\lt\top in the category \cattwo to
the function \emptyset \to 1=\{\emptyset\} in \Set.
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