noun

- (used with a plural verb) Logic. two laws, one stating that the denial of the conjunction of a class of propositions is equivalent to the disjunction of the denials of a proposition, and the other stating that the denial of the disjunction of a class of propositions is equivalent to the conjunction of the denials of the propositions.
- (used with a singular verb) Mathematics.
- the theorem of set theory that the complement of the union of two sets is equal to the intersection of the complements of the sets.
- the theorem of set theory that the complement of the intersection of two sets is equal to the union of the complements of the sets.

pl n

- (in formal logic and set theory) the principles that conjunction and disjunction, or union and intersection, are dual. Thus the negation of P & Q is equivalent to not-P or not-Q