Editing Double counting (proof technique) (section)

===Related topics===
* [[Bijective proof]]. Where double counting involves counting one set in two ways, bijective proofs involve counting two sets in one way, by showing that their elements correspond one-for-one.
* The [[inclusion–exclusion principle]], a formula for the size of a [[Union (set theory)|union]] of sets that may, together with another formula for the same union, be used as part of a double counting argument.