“…Thus, given a formula graph for a cell X that references Y, du-adequacy is achieved with respect to the interactions between X and Y when each of X's uses (references to Y) 1 of each definition in Y (node directly connected to the exit node in Y's formula graph) has been covered by a test. For example, the du-associations involving Abbott's Final cell (Grades [1,3]) and his Course cell (Grades [1,4]) are (2,5)T, (2,5)F, (2,6), and (2,7), using the node numbers in Figure 2. Hence, under the du-adequacy criterion, Grades [1,4] is tested enough when there has been a successful test in which Grades [1,3] was greater than Grades[1,2]-covering du-associations (2,5)T and (2,6), -and another test in which Grades [1,3] was not greater than Grades[1,2]-covering du-associations (2,5)F and (2,7).…”