1: Fundamentals
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- 1.3: Combinations and Permutations
- We turn first to counting. While this sounds simple, perhaps too simple to study, it is not. When we speak of counting, it is shorthand for determining the size of a set, or more often, the sizes of many sets, all with something in common, but different sizes depending on one or more parameters.
- 1.7: The Pigeonhole Principle
- A key step in many proofs consists of showing that two possibly different values are in fact the same. The Pigeonhole principle can sometimes help with this.