One can distinguish direct fusion, indirect fusion and fusion of the outputs of the former two.

一个融合处理过程可以识别直接融合，间接融合及前两者的输出的融合。

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So the later two kinds of direct outputs and the indirect profits are the positive externalities of metro projects.

直接产出中的后两类和间接产出都属于地铁项目的正外部性。

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