16 Two characters Allow characters can be unordered and have an arbitrary number of states, but restrict on the maximum number of characters two Definition 6.2 A triangulated graph is an undirected graph in which any cycle with four or more vertices has a chord, that is, an edge joining two nonconsecutive vertices of the cycle Theorem 6.1 To every collection of subtrees (T 1, T 2, ..., T l ) of a tree T there corresponds a triangulated graph and vice versa