Why use Set Theory, when we can use Lisp?

How can I prove that math is not a pseudoscience?

>>9
define "contain"
Include its reference in the hash map.

define "contain itself"
Include in the hash map a reference to itself.

define "set"
Hash map of keys without associated values.

define "set of sets"
Set whose hash map contains references to other sets (which better be immutable).

Now you define "define".