- Now the bottom-- the little underscore in the bottom right hand corner represents the blank tile and just as with my thumbs I would move 4 down or maybe 2 to the right.

现在下方,右下方的下划线表示空白片,我可以用手指将4移下来,或者将2移到右边。

哈佛公开课 - 计算机科学课程节选