如果你那里的天气适合户外活动，我强烈推荐这种粉笔数学法。
If your weather is nice enough to get outside I highly recommend sidewalk chalk math.
在物理学的数学法则里，没有什么规定说时间只能往前走。
And there's nothing in the mathematical laws of physics that says time can only go forward.
数学法则用在现实中是不确定的，确定的时候，又不能用于现实。
As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality.
应用推荐