ELI5: Explain Like I'm 5

Peano arithmetic

Peano arithmetic is like a game of counting, but with some special rules. We start with the number 0 and then count up by adding 1 each time. We can also add any two numbers together, which gives us a new number. For example, if we add 3 and 2, we get 5.

But Peano arithmetic also has some other special rules that make it more interesting. For one, Peano arithmetic has something called the successor function. This function takes a number and adds 1 to it to give us the next number in the sequence. So, if we start with 0 and apply the successor function, we get 1. If we apply it again, we get 2, and so on.

Another special rule is that we can define addition and multiplication using the successor function. For example, to add 2 and 3 in Peano arithmetic, we can apply the successor function three times to the number 2 (which gives us 5). We can also define multiplication as repeated addition. So, to multiply 2 and 3, we can add 2+2+2, which gives us 6.

Finally, Peano arithmetic also has some rules about how numbers relate to each other. For example, we can say that any number added to 0 is itself. We can also say that any number added to its successor is one more than that number. So, 2+1=3, 3+1=4, and so on.

Overall, Peano arithmetic is a fun and interesting way to think about numbers and math. It lets us play with numbers in new ways and discover new things about them.