如果X是一个子集，但不确定他们是等价的集合，那么用一条加亮的点线连接他们。
If X is a subset, but it is unknown whether they are equal sets, then the line is lighter and is dotted.
点到点线路直接连接发送和接收设备，而多点线路连接多个设备，而不仅仅是一个发送方设备和一个接收方设备。
A point-to-point line directly connects the sending and the receiving devices, and a multidrop line connects many devices, not just one sending device and one receiving device.
为了安装以及检修的方便，在电气原理图中元件的连接点线往往都应该标有编号。
In order to facilitate the installation and maintenance of the electrical components in the principle of the connection point line often be marked with code.
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