21: Permutations
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- 21.1: Factorials
- In counting, factorials come up a lot.
- 21.2: Definition
- We often want to count how many ways we can “mix up” the objects in a collection.
- 21.3: Counting Permutations
- For |A|=n, there are n! permutations on A.
- 21.4: Permutations of Subsets
- Sometimes we want to create an ordered list of a certain length from a larger pool of candidates.