\begin{definition}[Definition:Inverse Square Law]
Two real variables $x$ and $y$ are related by an '''inverse square law''' {{iff}} they fulfil the relationship:
:$\forall x, y \in \R: x \propto \dfrac 1 {y^2} \iff \exists k \in \R, k \ne 0: x y^2 = k$
\end{definition}