要理解递归，首先必须理解递归。

In three words I can sum up everything I've learned about life: it goes on.

If you have an apple and I have an apple, and we exchange apples, we both still only have one apple. But if you have an idea and I have an idea, and we exchange ideas, we each now have two ideas.

I don't want to be a star, I want to be a legend.

Find your enemy, you will be safely!