$\phi \land \psi \equiv \lnot (\lnot \phi \lor \lnot \psi) \equiv \lnot (\phi \implies \lnot \psi)$
↧
$\phi \land \psi \equiv \lnot (\lnot \phi \lor \lnot \psi) \equiv \lnot (\phi \implies \lnot \psi)$