ELI5: Explain Like I'm 5

Denjoy–Riesz theorem

Okay, kiddo! Let's talk about the Denjoy-Riesz theorem. Imagine you are playing with a slinky toy, you can stretch it, twist it, and pull it. Similarly, mathematicians have a tool called "Curve", it is like a slinky toy, but they use it to draw lines on a piece of paper. But sometimes some curves can be naughty, meaning they might not be drawn the way mathematicians want them to be drawn.

So, the Denjoy-Riesz theorem tells us that even the naughtiest and weirdest curves can be broken down into easier curves called "Rectifiable Curves". This means we can make them straightened out like a ruler by moving them around with a ruler and a compass, just like you straighten a slinky toy by pulling it with your hands.

This might seem simple, but it's super important for mathematicians when they are trying to solve complex equations and understand curves. So, whenever you see a slinky toy, remember the Denjoy-Riesz theorem and the power of straightening out naughtiest curves!