Let and be relations on sets and respectively.
The structure is:
1). extensional if ,
Show that if and are extensional and well-founded, then there is at most one isomorphism between them.
Hint: Consider for an automorphism of .
I have absolutely no idea how to do this question. I can't see how the hint is helpful. If I consider the automorphism, i'm not considering which I need to do.
Can anyone point me in the right direction?