ELI5: Explain Like I'm 5

Kawasaki's Riemann–Roch formula

Imagine you have a big playground with lots of swings and slides. Each swing and slide has a number on it, which tells you how many times you can go on it before you get tired. Now imagine that you are a group of friends who want to play on all the swings and slides. You want to know how many times you can play on all the swings and slides combined, without getting tired.

This is kind of like what the Riemann-Roch formula does - it helps us to count how many times we can play on certain mathematical objects without getting "tired". But instead of swings and slides, we're talking about curves (which are kind of like squiggly lines) on a surface called a manifold. And instead of getting tired, we're using fancy math terms to describe whether or not these curves "vanish" or "grow" at different points on the surface.

To make things a bit more complicated, we need to use some special math tools called divisors, which are like "counting tools" that help us keep track of which curves we're talking about and how many times we're playing on them. So, just like you might count how many times you've gone down a slide by marking it with a tally mark, we use divisors to count how many times we've gone around a curve on the manifold.

Now, here's the cool part: the Riemann-Roch formula tells us that if we add up the number of times we can play on certain curves (as counted by our divisors), and subtract the number of times those curves "vanish" or "grow" at different points on the manifold (which is called the "degree" of the divisor), we get a special number that tells us how many times we can play on all the curves combined. It's kind of like a "score" that helps us understand how the curves are behaving on the manifold.

So essentially, the Riemann-Roch formula is a powerful tool that helps us to understand the relationship between curves on a manifold, and gives us a way to count how many times we can "play" on these curves without getting tired. It's a bit complicated, but with the right tools (like divisors and degree), we can use this formula to unlock a whole world of mathematical understanding!