## FANDOM

1,025 Pages

The inclusion-exclusion principle is a combinatoric principle that states the cardinality of the union of any two sets is equal to the sum of their cardinals minus the intersection of those sets. This can be expressed symbolically as $|A\cup B|=|A|+|B|-|A\cap B|$ . If the two sets are disjoint, then this can be simplified as the Rule of sum.