Since exchange are named entities the attempt to declare a previously existingexchange with a different type results in an error.
因为交换器是命名实体，所以声明一个已经存在的交换器，但是试图赋予不同类型是会导致错误。
2
As you see, after establishing the connection we declared the exchange. This step is necessary as publishing to a non-existingexchange is forbidden.
如亲所见，建立连接后我们声明了一个交换器。因为发布消息到不存在的交换器是禁止的，所以这步是必须的。
3
This essay is aimed to describing the existingexchange rate systems, their impact on local and international economy and analysis of pros and cons of each system.