De Morgan's Laws

Rules in propositional logic and set theory stating that the negation of a conjunction equals the disjunction of the negations, and the negation of a disjunction equals the conjunction of the negations (¬(A∧B) ⇔ ¬A∨¬B and ¬(A∨B) ⇔ ¬A∧¬B), with corresponding set complement analogues.

The pair of logical equivalences that relate negation with conjunction and disjunction: ¬(A ∧ B) is equivalent to (¬A) ∨ (¬B), and ¬(A ∨ B) is equivalent to (¬A) ∧ (¬B) in classical logic and Boolean algebra.

Two algebraic rules that describe how complementation (logical negation or set complement) distributes over the binary operations of union and intersection (or OR and AND): the complement of a union equals the intersection of the complements, and the complement of an intersection equals the union of the complements.