Labeled tree, Labelled tree

Labeled tree, Labelled tree --- помеченное дерево. A labeled tree is a tree whose nodes are labeled from a finite alphabet [math]\displaystyle{ \Sigma }[/math]. An unordered labeled tree is just a rooted labeled tree. An ordered labeled tree is a rooted labeled tree in which the children of each node are ordered, i.e., if a node has [math]\displaystyle{ k }[/math] children, then we can specify them as the first child, the second child, \ldots, and the [math]\displaystyle{ k }[/math]th child.