“…The graph H 4 (K 4 ) is constructed by replacing the vertices x ij0 , i = 0, 1, j = 0, 1, 2 with the vertices of one stable set of B 6,6 , and the vertices x ij0 , i = 2, 3, j = 0, 1, 2 with the vertices of the other stable set of B 6,6 ; see Figure 6. Observe that the vertex x is depicted in two places, so that the graph can be more easily drawn.…”