ELI5: Explain Like I'm 5

(2,3,7) triangle group

A triangle group is like a special type of club where everyone in the club has to follow a certain set of rules. The (2,3,7) triangle group is a club where the rules are based on three numbers - 2, 3, and 7.

Imagine you have three friends - let's call them A, B, and C. You want to make a special club with them that has rules based on these numbers. Here's how it works:

- The number 2 means that each person in the club has to be able to do two things. Let's say the two things are standing on one foot and clapping their hands.
- The number 3 means that any three people in the club have to be able to stand in a circle with their arms around each other's shoulders. This is important because it helps the club members work together.
- The number 7 means that the club has to be "as big as possible" without breaking the other rules. So, you can't have six people in the club because three can't stand in a circle (rule 2), and you can't have eight people because it's not as big as possible (rule 3).

The (2,3,7) triangle group has rules like this, but with math instead of standing on one foot and clapping. Specifically, the rules have to do with how you can "connect" sides of a triangle. If you draw a triangle on a piece of paper, each side of the triangle is like a line. Now, imagine you want to "connect" these lines. There are rules for how you can do that in the (2,3,7) triangle group.

In plain English, this means that if you have three lines, there are only certain ways you can connect them to make a triangle that follows the rules of the (2,3,7) triangle group. This is important in math because it helps us understand how shapes can be connected and how they behave when we make connections.