---
Set (message='My nested sets'):
  Set#size: 3
  Element 0: Fixnum 0
  Element 1:
    Set:
      Set#size: 2
      Element 0: Fixnum 1
      Element 1: Fixnum 2
  Element 2:
    Set:
      Set#size: 2
      Element 0: Fixnum 3
      Element 1: Fixnum 4