Comment Comment by denotational > Yes -- in set theory sets can contain themselvesWhich set theory? ZFC doesn't permit this.Non-well-founded set theories are so non-standard that I think it's wrong, or at least misleading, to claim that unqualified "set theory" permits this. parent denotational 7 months ago
Which set theory? ZFC doesn't permit this.
Non-well-founded set theories are so non-standard that I think it's wrong, or at least misleading, to claim that unqualified "set theory" permits this.