\begin{definition}[Definition:Binding Constraint]
Let $\RR$ be a weak inequality on some set $S$.
Let $a \mathrel \RR b$ be a constraint given by a weak inequality $\RR$.
Let $P \in S$ such that $P \mathrel \RR b$ is an equality.
Then $a \mathrel \RR b$ is '''binding''' at $P$.
\end{definition}