“…Observe that the equivalence classes of the relation ↔ are E 1 = {(1, 2), (1, 3), (1, 4), (5, 4), (6, 4)} and E 2 = {(2, 1), (3, 1), (4, 1), (4,5), (4, 6)}. By using two permutation P and Q to move rows 1, 5, 6 (the white nodes of E 1 ) on the top of the matrix and rows 2, 3, 4 (the white nodes of E 2 ) on the bottom and to move columns 2, 3, 4 (the black nodes of E 1 ) on the left and columns 1, 5, 6 (the black nodes of E 2 ) on the right we obtain …”