module Doubler
  def double
    self + self
  end
end

class String
  include Doubler

  # for a good time...
  # def method_missing x
  #   self + x.to_s
  # end
end

class Name
  include Comparable

  attr_accessor :first, :last

  def initialize (first, last)
    @first = first
    @last = last
  end

  def <=> other
    ans = last <=> other.last
    return ans if ans != 0
    first <=> other.first
  end
end

class BinaryTree
  include Enumerable

  attr_accessor :left, :data, :right

  def initialize(l, x, r)
    @left = l
    @data = x
    @right = r
  end

  # in section AB, we had left the method_missing on String trick above,
  # which caused problems in irb itself :(
  #
  # the following code is actually fine
  def each
    left.each { |x| yield x } unless left.nil?
    yield data
    right.each { |x| yield x } unless right.nil?
  end
end