I already mentioned that. It's like the ground floor.

我之前已经提到过这个，它就像是楼房的一楼。

麻省理工公开课 - 固态化学导论课程节选

But mathematically, we've mentioned this before, log N or really to be precise, log base 2 of N, is the way you express this mathematically.

但从数学上说，之前我们已经提到过了，准确地说是log，N，以2为底N的对数，这就是它在数学上的表示。

哈佛公开课 - 计算机科学课程节选