\item for every $\begin{tikzcd} A \ar[r,bend left,"u",""{name=A,below}]\ar[r,bend right,"v"',""{name=B,above}]& B \ar[from=A,to=B,Rightarrow,"\alpha"]\end{tikzcd}$ in $\CCat$,
is fully faithful and its essential image consists of morphisms of op-prederivators $F : \C\to\sD$ such that for every small category $A$, $F_A : \C(A)\to\sD(A)$ sends morphisms of $\W_A$ to isomorphisms of $\sD(A)$.
This universal property is a higher version of the universal property of localization seen in \ref{paragr:loc}. It follows that given two localizers $(\C,\W)$ and $(\C',\W')$ and a functor $F : \C\to\C'$, if $F$ preserves weak equivalences, then there exists a morphism of op-prederivators $\overline{F} : \sD_{(\C,\W)}\to\sD_{(\C',\W')}$ such that the square
Let $(\C,\W)$ and $(\C',\W')$ be two localizers. A functor $F : \C\to\C'$ is \emph{left derivable in the sense of derivators} if there exists a morphism $\LL F : \sD_{(\C,\W)}\to\sD_{(\C',\W')}$ and a $2$-morphism