ELI5: Explain Like I'm 5

Nikodym set

Okay kiddo, imagine you have a big basket of marbles. Some of the marbles are red and some are blue, but you don't know how many of each color there are.

Now imagine someone comes along and tells you that there are exactly two times as many red marbles as there are blue marbles.

This information helps you figure out how many of each color there are! If you have 2 blue marbles, then you must have 4 red marbles. If you have 4 blue marbles, then you must have 8 red marbles. And so on.

Now, let's say you have another basket of marbles, but this time it's much bigger and has a lot of different colors. You still don't know how many of each color there are, but someone gives you some information that helps you figure it out.

This information is like the Nikodym set. It's a mathematical concept that helps you understand the structure of a set (like a group of marbles) even if you don't know exactly what's in it.

It's named after a mathematician named Otto Nikodym, who came up with the idea in the early 1900s.

Basically, when we talk about a Nikodym set, we're talking about a way of breaking down a larger set into smaller parts, each of which has its own measure (like the number of marbles in a color).

By doing this, we can get a better understanding of the larger set, even if we don't actually know everything about it. It's like breaking down the big basket of marbles into smaller piles, where you can count how many red and blue ones there are in each pile.

So, a Nikodym set is a way of thinking about the structure of a set, even if we don't have all the information about it. It's a tool that mathematicians use to help solve problems and understand complex systems.