Definition:Rooted Tree/Descendant

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Let $T$ be a rooted tree with root $r_T$.

Let $t$ be a node of $T$.

A descendant node $s$ of a $t$ is a node such that $t$ is in the path from $s$ to $r_T$.

That is, the descendant nodes of $t$ are all the nodes of $T$ of which $t$ is an ancestor node.

Proper Descendant

A proper descendant node of $t$ is a descendant of $t$ which is not $t$ itself.

Also see

  • Results about descendant nodes can be found here.