# File Ouroboros.rb, line 325
  def adjacent_duplicates?( &obj_indexer )
    keys = {}
    @all.each{ |list_item|
      keys[list_item] = block_given? ? yield(list_item) : list_item
    }
    @all.each{ |o|
      return true if keys[o]==keys[o.next]
    }
    return false
  end