Google is failing me in my search for examples of identical sets which do no have causal relationships between them. What I mean is that all and only objects which belong to set A belong to set B, but an object being in set B is not caused by its being in set A, nor is an object being in set A caused by its being in set B.
My prof said she heard of something once that went along the lines of "set A = animals that have a spleen, set B = animals that have a different organ" but she couldn't remember the exact details, and I can't seem to find what she was talking about (I don't know enough biology to say off the top of my head)...
Can anyone think of examples?
Thanks in advance :)