“…Since no edge of P extends to a triangle, implications (3), (4) show that none of {0, 2}, {1, 3}, {2, 4} can belong to P and implications ( 5), (6) show that neither of {0, 3}, {1, 4} can belong to P . Hence each of the three edges of P must be one of {0, 1}, {1, 2}, {2, 3}, {3, 4}, {0, 4}.…”