De Morgan Laws

Definition

Let $(A,\vee ,\wedge )$ be a Lattice. Then $\neg :A\to A$ is a De Morgan involution iff

$$\begin{array}{rl}\neg (x\vee y)& =\neg x\wedge \neg y\\ \neg (x\wedge y)& =\neg x\vee \neg y\\ \neg \neg x& =x\end{array}$$