\begin{definition}[Definition:Rooted Tree/Child Node/Grandchild Node]
Let $T$ be a rooted tree with root $r_T$.
Let $t$ be a node of $T$.
A child of a child node of a node $t$ can be referred to as a '''grandchild node''' of $t$.
In terms of the parent mapping $\pi$ of $T$, a '''grandchild node''' of $t$ is a node $s$ such that:
:$\pi \left({\pi \left({s}\right)}\right) = t$
Category:Definitions/Rooted Trees
\end{definition}