Formal Notation
The negation of conjunction rule may be written in sequent notation:
The negation of disjunction rule may be written as:
In rule form: negation of conjunction
and negation of disjunction
and expressed as a truth-functional tautology or theorem of propositional logic:
where, and are propositions expressed in some formal system.
Read more about this topic: De Morgan's Laws
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—Marcel Proust (1871–1922)