ELI5: Explain Like I'm 5

Postnikov system

A postnikov system is like a special way of building things, but instead of using regular building blocks, we use different levels of information. It's like building with different layers of knowledge or understanding.

Imagine you want to build a big tower, but you can't do it all at once. So you start with a small base, and as you go higher, you add more and more layers on top of each other, each layer making the tower taller and more complete.

In a postnikov system, it's sort of the same idea but with information instead of physical layers. Let's say you have some mathematical object, like a shape or a structure. Instead of knowing everything about it all at once, you can learn about it one layer at a time. Each layer gives you more details and a better understanding of the object.

But how do we make these layers of information? Well, mathematicians use something called homotopy theory. It's like a special kind of math that deals with spaces and how they can change or transform into one another. With homotopy theory, we can study the different ways that objects can be similar or different from each other.

So, to build our postnikov system, we start with the simplest layer, called the zeroth layer. This layer tells us some basic information about the object. But it's not complete, so we add another layer, called the first layer, which gives us more details, like how the object might be curved or twisted in some way. And then we can keep adding more and more layers, each one revealing more about the object.

The goal of a postnikov system is to keep adding layers until we have learned everything there is to know about the object. But sometimes, we might not be able to reach the very top. In those cases, we can still learn a lot and understand the object pretty well with the information we have.

So, just like building a tower with different layers, a postnikov system helps us understand mathematical objects by studying them one layer at a time. It's a way for mathematicians to explore and uncover the mysteries of these objects and how they relate to each other.