It looks like a tautology because you're never able to show me something that moves forever at a constant velocity, because every time you don't find such a thing, I give an excuse, namely, a force is acting.

这听上去像个死循环,因为你不可能,找到永远匀速运动下去的物体,因为每当你找不到这样的物体时,我就会给出一个理由,也就是,有力作用在上面

耶鲁公开课 - 基础物理课程节选

If it isn't, then I'm going to go back around the loop, and notice what happens. If I get all the way around the loop, that is, all the way through that FOR loop and I never find a path that takes me through here, then the last thing I'm going to do is return a pair or a tuple with a special simple number none twice.

如果没有,我会回到循环看看发生了什么,如果我运行了整个循环,也就是整个for循环,我仍没有找到符合条件的路径,那么我最后做的事情就是返回一对,或者一个数组的两次none值。

麻省理工公开课 - 计算机科学及编程导论课程节选