Internal vertex of a rooted tree
= Internal vertex of a rooted tree
= Internal vertices of a rooted tree
{synonym}
A <vertex> with at least one <child in a rooted tree>. Internal <vertices> and <leaves of a rooted tree> partition the <vertex set>. The ancestors of an internal <vertex> are also internal; consequently the internal <vertices> of a nontrivial <rooted tree> induce a connected <subgraph> containing its root.