It isn’t even ever true for finite sets, except by convention for the empty set.
I think that you’re confusing the element-of relation with the subset-of relation. Or something. But then, all sets are subsets of themselves, including finite ones, so I’m not sure what you were thinking.
At any rate, the empty set is not an element of itself according to any convention that I’ve ever seen.
You aren’t going to find the X that satisfy member(X,X) by unification.
I’m not sure how to respond to this until you answer my question in this comment.
I think that you’re confusing the element-of relation with the subset-of relation. Or something. But then, all sets are subsets of themselves, including finite ones, so I’m not sure what you were thinking.
At any rate, the empty set is not an element of itself according to any convention that I’ve ever seen.
I’m not sure how to respond to this until you answer my question in this comment.
You’re right; I was mis-remembering. It can’t be, or 1 := 0 u {0} wouldn’t work.