\begin{definition}[Definition:Dual Relation/Inverse of Complement]
Let $\RR \subseteq S \times T$ be a binary relation.
Then the '''dual''' of $\RR$ is denoted $\RR^d$ and is defined as:
:$\RR^d := \paren {\overline \RR}^{-1}$
where:
:$\overline \RR$ denotes the complement of $\RR$
:$\paren {\overline \RR}^{-1}$ denotes the inverse of the complement of $\RR$.
\end{definition}