Chứng minh rằng:  $ p \Rightarrow (q \Rightarrow r) \equiv ( p \wedge q) \Rightarrow r $

Ta có:
$ \begin{array}{l}
p \Rightarrow \left( {q \Rightarrow r} \right) \equiv \bar p \vee \left( {q \Rightarrow r} \right)\\
 \equiv \bar p\left( {\bar q \vee r} \right)\\
 \equiv \left( {\bar p \vee \bar q} \right) \vee r\\
 \equiv \overline {\left( {p \wedge q} \right)}  \vee r\\
 \equiv \left( {p \wedge q} \right) \Rightarrow r
\end{array} $