ELI5: Explain Like I'm 5

Dedekind-Kummer theorem

Okay, so imagine you have a bunch of numbers, like 1, 2, 3, 4, 5, etc. These are called "natural numbers." But what happens when you want to do math with other types of numbers, like fractions (1/2, 3/4, etc.), or negative numbers (-1, -2, etc.)? Well, there are rules and tricks for doing math with these types of numbers, and we call this "abstract algebra."

One thing we can do in abstract algebra is called "factoring." This means we break down a big number into smaller parts that we can multiply together to get the big number again. For example, 12 can be factored into 2 x 2 x 3. But what if we're working with strange types of numbers that don't necessarily follow the rules we're used to? That's where the Dedekind-Kummer theorem comes in.

The Dedekind-Kummer theorem is a fancy math idea that says that certain types of numbers called "prime ideals" can be factored in a similar way to regular numbers, even in weird algebraic systems. Okay, so what's a prime ideal? Imagine you have a "ring," which is really just a set of numbers that follow certain rules when you add, subtract, and multiply them. We call it a "ring" because you can imagine the numbers lining up in a circle like a ring.

When we look at certain types of rings, like the "ring of integers" or the "ring of polynomials," we can talk about "ideals." Ideals are like special types of sets of numbers that have some special properties. For example, in the ring of integers, the ideal (2) contains all the even numbers. Larger sets of numbers can be made up of smaller ideals combined together, kind of like how you can make the number 12 by multiplying together the smaller numbers 2, 2, and 3.

Now, when we're looking at "prime ideals," we're talking about sets of numbers that can't be broken down any further. Just like the number 7 is prime because you can't break it down into any smaller parts (it's just 7), prime ideals are special because they can't be split up into smaller ideals. When we try to "factor" a prime ideal, we're really just looking for a bunch of other (non-prime) ideals that we can multiply together to get the prime ideal.

The Dedekind-Kummer theorem says that we can do this factorization in certain types of rings, even when the numbers inside the rings don't follow the usual rules we're used to for numbers. This is really helpful in understanding algebraic systems that might be really complicated or hard to work with, because we can break them down into smaller parts and study them one piece at a time.