ELI5: Explain Like I'm 5

Constant rank theorem

The constant rank theorem is like when mommy bakes a cake. She knows if she puts in a certain amount of flour, sugar and eggs, then the cake will come out looking and tasting just right. This is because she has a recipe that always works.

Similarly, when grown-up math people want to know things about shapes, like how round or curved they are, they use a special recipe called the constant rank theorem. The recipe tells them how these shapes behave in different directions, and what their exact size, or “rank,” is.

The theorem works like this: imagine you have two different shapes, and you stretch and twist them around in all different ways. The theorem says that if you compare how curved or round they are in all the different directions, you’ll always get the same answer. It’s like saying a cake is just as tasty and fluffy when you cut it horizontally or vertically.

This is really helpful for math people because they can use the constant rank theorem to figure out a lot of things about the shapes they study. They can even use it to make new shapes that behave in the same way as the old ones, just like mommy can use the same cake recipe to make lots of different cakes. So the constant rank theorem is kind of like a secret recipe for understanding and making certain shapes in math.
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