# File lib/unified_ruby.rb, line 250
  def rewrite_flip2(exp)
    # from:
    # s(:flip2,
    #   s(:call, s(:lit, 1), :==, s(:arglist, s(:gvar, :$.))),
    #   s(:call, s(:lit, 2), :a?, s(:arglist, s(:call, nil, :b, s(:arglist)))))
    # to:
    # s(:flip2,
    #   s(:lit, 1),
    #   s(:call, s(:lit, 2), :a?, s(:arglist, s(:call, nil, :b, s(:arglist)))))
    exp[1] = exp[1][1] if exp[1][0] == :call && exp[1][1][0] == :lit
    exp
  end