So this we would want to delete in order for the code not to run the risk of crashing, but let's now see this was made by an excellent teacher out at Stanford University.

我要按顺序删除它，不要冒崩溃的风险,但是这个是由一个来自斯坦福大学的,优秀教师做的。

哈佛公开课 - 计算机科学课程节选