<Li> ∩ is the intersection, and </Li> <Li> ∪ is the union . </Li> <P> In formal language, the rules are written as </P> <Dl> <Dd> ¬ (P ∨ Q) ⟺ (¬ P) ∧ (¬ Q), (\ displaystyle \ neg (P \ lor Q) \ iff (\ neg P) \ land (\ neg Q),) </Dd> </Dl>

Not a and not b or a and b