\begin{definition}[Definition:Null Relation]
The '''null relation ''' is a relation $\RR$ in $S$ to $T$ such that $\RR$ is the empty set:
:$\RR \subseteq S \times T: \RR = \O$
That is, ''no'' element of $S$ relates to ''any'' element in $T$:
:$\RR: S \times T: \forall \tuple {s, t} \in S \times T: \neg s \mathrel \RR t$
\end{definition}