ELI5: Explain Like I'm 5

Normal form for free groups and free product of groups

Okay, kiddo, let's learn about normal form for free groups and free product of groups!

First, let's talk about what a group is. A group is like a special team where all the members follow certain rules when they work together. These rules are called group axioms. The members of a group are called elements, and they can do special things like combining with each other to make new elements.

Now, a free group is a group where the elements are made up of letters, kind of like how you put letters together to make words. The free part means that we can make any combination of letters we want to make a new element. For example, we can take the letters "a" and "b" and combine them to make a new element "ab". We can also take the letter "a" and its inverse, "a^-1", and combine them to make the identity element "e" (which is like zero in regular math).

But sometimes we have different ways of combining the letters that give us the same element. For example, "ab" and "ba^-1" are actually the same element, even though they use different letters. So, we want to find a way to write each element in a unique way.

This is where normal form comes in. The normal form for a free group is an expression for an element that we've simplified as much as possible. This means we've combined any inverse elements with their corresponding letters and we've put the letters in a certain order. We can also choose to exclude certain combinations of letters that cancel out, like "aa^-1".

Now, let's talk about the free product of groups. This is when we take two or more different groups and combine them together to make a new group. It's like making a team with players from different teams. However, we have to be careful when we combine these groups, because sometimes elements from one group might not work well with elements from another group.

So, to make the free product, we take an element from each group and combine them together using a special symbol called the product symbol (*). We do this for every possible combination of elements, and then we simplify the expression using the normal form we learned about earlier.

For example, if we have two free groups, one with elements "a" and "b" and the other with elements "x" and "y", then the free product of these groups would have elements like "ax", "by", "xy", and so on. We'd simplify these elements by using the normal form, which might mean putting the letters in a certain order and combining inverse elements.

So, in summary, the normal form for a free group is an expression for an element that we've simplified as much as possible, and the free product of groups is when we take two or more different groups and combine them together to make a new group, simplifying the expression using the normal form. Alright, high-five for learning something new today!