A cardinal tree (or trie) of degree k, by analogy with cardinal numbers and by opposition with ordinal trees, is a rooted tree in which each node has k positions for an edge to a child.^[1] Each node has up to k children and each child of a given node is labeled by a unique integer from the set {1, 2, . . . , k}. For instance, a binary tree is a cardinal tree of degree 2.