code: def EXCHANGE(classical_reg1, classical_reg2):
      
      left = unpack_classical_reg(classical_reg1)
      right = unpack_classical_reg(classical_reg2)
      return ClassicalExchange(left, right)
docs: Produce an EXCHANGE instruction.
  
      :param classical_reg1: The first classical register, which gets modified.
      :param classical_reg2: The second classical register, which gets modified.
      :return: A ClassicalExchange instance.