I going to come back in a second to how it actually does that, but it basically says, get me x value for p 1, get me the x value for p 2, compare them, just as you would normally.

是一个类的实例,我要去取的这个实例，所关联的x值，我稍后会讲讲实际上，这里是怎么实现的，但是基本上它的意思就是，给我p1的x值。

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