A directed graph.
A pair of letters, especially a pair representing a single phoneme.
A two-character sequence used to enter a single conceptual character.
a sequence of two lines, each of which may be unbroken, broken once, or broken twice.
A graph in which the edges are ordered pairs, so that, if the edge (a, b) is in the graph, the edge (b, a) need not be in the graph and is distinct from (a, b) if it is.