\begin{definition}[Definition:Inverse Entourage]
Let $S$ be a set.
Let $\UU$ be a quasiuniformity on $S$.
Let $u \in \UU$ be an entourage of $\UU$.
Then the '''inverse entourage''' $u^{-1}$ is defined as:
:$u^{-1} := \set {\tuple {y, x}: \tuple {x, y} \in u}$
\end{definition}