•Let f be an invariant.
•Suppose two objects, A and B have a common image.
Then f(I)=f(J) if I and J are images of
either A or B.
•Given any O0, Ok, we construct a series of objects, O1, …, O(k-1), so that Oi and O(i+1) have a common image for all i, and Ok and j have a common image.
•So for any pair of images, I, J, from any two objects, f(I) = f(J).