If (a, b) is a (directed) arc in a digraph D we say that a is ‘adjacent to’ b, or that 6 is ‘adjacent from’ a. If the arcs (a, b) and (b, a) are both present in D we say, for brevity, that a is ‘adjacent with’ b or that a and b are ‘adjacent both ways’. If neither (a, b) nor (b, a) occur, a and b are ‘non-adjacent’. A digraph C is transitive if the… (More)