If you think of these kind of like trays in a cafeteria, right, that are kind of upside down, and by default, they're stacked from the floor on up and up and up.

如果你想象这种自助餐厅的托盘，对的，那有点混乱的，默认的，它们从地板开始往上堆起来。

哈佛公开课 - 计算机科学课程节选