Arc Consistency Propagation
	n When we remove a value from Dx, we may get new removals because of it n E.g. Dx = {1,4,5}, Dy = {1, 2, 3}, Dz= {2, 3, 4, 5} n x > y,  z > x n As before we can remove 1 from Dx, so Dx = {4,5} n But now there is no support for Dz = 2,3,4 n So we can remove those values, Dz = {5}, so z=5 n Before AC applied to y-x, we could not change Dz n This can cause a chain reaction