# Homework Help: Explain this to me as if I were 5 years old

1. Jul 27, 2010

### Jamin2112

1. The problem statement, all variables and given/known data

5.10. Definition. A permutation of a finite set S is a bijection from S to itself. The word form of a permutation of [n] is the list obtained by writing the image of i in position i. We write n!, read as "n factorial", to mean n*(n-1)*(n-2)* ... *2*1.

2. Relevant equations

None

3. The attempt at a solution

Please explain the mumbo jumbo before the last sentence.

2. Jul 27, 2010

### Office_Shredder

Staff Emeritus
For example, a permutation of the set {1,2,3} could be a function f(x) where f(1)=1, f(2)=3 and f(3)=2. By the word form we can write this permutation as 1 3 2. The number 1 is first so f(1)=1. The number 3 is second so f(2)=3. The number 2 is third so f(3)=2 (permutations are rarely denoted as f(x) but I do so here for the sake of clarity)

If you were given the permutation f(x) described by 2 5 3 4 1, then f(1)=2 since the first number listed is a 2, and f(2)=5 since the second number listed is a 5