def mix_c!(i, j, c = nil)
      @body.mix_c!(i, j, c)
      @right.mix_c!(i, j, c)
      self
    end
def mix_c!(i, j, c = nil)
      @body.mix_c!(i, j, c)
      @right.mix_c!(i, j, c)
      self
    end
def mix_r(i, j, c = nil)
    dup.mix_r!(i, j, c)
  end