Roy's identity
Roy's identity is a fancy way of saying that when you add two things together and then take away one of them, it's the same as if you started with the first thing and then added the difference between the first and second thing.
For example, let's say you have 7 jellybeans and you add 5 more jellybeans. Now you have 12 jellybeans. But if you take away 5 of those jellybeans, you'll be left with 7 jellybeans - which is the same as what you started with!
This is called Roy's identity because it was discovered by a mathematician named Roy Langlands. He found out that this works for more than just jellybeans - it's true for lots of different mathematical problems too!
For example, let's say you have 7 jellybeans and you add 5 more jellybeans. Now you have 12 jellybeans. But if you take away 5 of those jellybeans, you'll be left with 7 jellybeans - which is the same as what you started with!
This is called Roy's identity because it was discovered by a mathematician named Roy Langlands. He found out that this works for more than just jellybeans - it's true for lots of different mathematical problems too!