If $X$, $Y$, $Z$ are objects of a topos $\ECat$, there exists a unique arrow from $\ObjMono{X}{Y}\times\ObjMono{Y}{Z}$ to $\ObjMono{X}{Z}$ factorizing the composition $\Con{C}$ from $Z\Sup{Y}\times Y\Sup{X}$ to $Z\Sup{X}$.

Proof. TODO

TODO