# Residue-class-wise affine group

Okay, let's pretend that you have a bunch of toys, and you want to organize them into groups. You can't just put all the toys together in one big pile – that would be chaotic and no fun to play with! Instead, you decide to group your toys according to their colors. So you put all the red toys in one pile, all the blue toys in another pile, and so on.

Now, let's imagine that instead of toys, you have numbers. And instead of colors, you're grouping them according to their remainders when you divide them by a certain number. For example, if you're working with numbers that are all multiples of 3, then you could group them according to their remainders when you divide by 3: 0, 1, or 2.

So you have three groups: the numbers that have a remainder of 0 when divided by 3, the numbers that have a remainder of 1, and the numbers that have a remainder of 2. These groups are called residue classes.

Now, let's imagine that you want to do some mathematical operations on these numbers in their respective residue classes. An affine function is a mathematical function that takes a number, multiplies it by another number, and then adds a third number to it. For example, if you multiply the number 2 by 3 and then add 1, you get 7. That's an affine function!

So, a residue-class-wise affine group is a mathematical group that works with these types of functions on numbers in residue classes. It's like a special set of rules for doing math with numbers that have the same remainder when divided by a certain number.

For example, imagine you're working with the residue classes of numbers that have a remainder of 2 when divided by 5. You could define a residue-class-wise affine group for these numbers by specifying a set of affine functions that take in a number in this residue class, do some multiplication and addition on it, and then give you back another number in the same residue class.

These functions might look like:

f(x) = 2x + 1
g(x) = 4x - 3

You could combine these functions in different ways – for example, by adding them together or composing them – to get new functions that still work within this same residue class. These new functions might look like:

h(x) = f(x) + g(x) = 6x - 2
i(x) = g(f(x)) = 8x - 5

And so on! The residue-class-wise affine group is like a set of tools that you can use to do math in a very specific way, with numbers that have the same remainder when divided by a certain number.