A mule is not spending 1/2 of its time as a donkey, and 1/2 of its time as a horse, we don't see it flickering back and forth between the two, that's not what we see.

骡子并不是一半的时间是驴，另一半的时间是马，我们不会看到它在两者之间来回变化，这不是我们所看到的情况。

麻省理工公开课 - 化学原理课程节选

John Now, you're going to hear John and I go back and forth a lot, well I'm certainly old time, but I'm also an old time Lisp programmer.

现在，你会听到我和,来回的讲好多次，好吧我当然是个老学究，但是我也是一个老lisp程序员。

麻省理工公开课 - 计算机科学及编程导论课程节选