\(\begin{aligned} & P\iff Q\\ \equiv\, & \left(P\implies Q\right)\wedge\left(Q\implies P\right)\\ \equiv\, & \left(\neg P\vee Q\right)\wedge\left(\neg Q\vee P\right)\\ \equiv\, & \neg\left(P\wedge\neg Q\right)\wedge\neg\left(Q\wedge\neg P\right) \end{aligned}\)