If you are not allowed to see other pieces of nature, it's a profound encounter and so beautiful.

但当你看不到其他的生物时，这种际遇就是那么深刻而美妙。

普林斯顿公开课 - 人性课程节选

If the time you are interested in is not zero, you're allowed to cancel it and get the time from here.

如果你们关注的解不是零时刻,那么就可以忽略它,然后从这里解出时间

耶鲁公开课 - 基础物理课程节选