ELI5: Explain Like I'm 5

Erdős–Szemerédi theorem

The Erdős–Szemerédi theorem is like a math puzzle about sets, which are groups of things. Imagine you have a big set of numbers, and you want to find a small set of numbers that has some special features.

One feature is that within this small set, any two numbers should be pretty far apart. Another feature is that this small set should be repeated many times throughout the bigger set.

The Erdős–Szemerédi theorem says that for any value of these features, you can always find a small set like this within the big set. It can be a little tricky to find it, but it will always exist.

This theorem is important because it helps mathematicians study patterns in big sets of numbers, and it has many practical applications in computer science and other fields.