Editing Negation normal form (section)

==Examples and counterexamples==
:{|style="float:right; margin: 1em;"
|<pre>
         ∨
       /   \
      ∧     D
    /   \
   ∧     ¬
 /   \   |
A     ∨  C
     /  \
    ¬    C
    |
    B         
</pre>
|}
The following formulae are all in negation normal form:
:<math>\begin{align}
&((A \lor B) \land C) \\
&(A \lor \lnot B) \\
&(A \land \lnot B) \\
&\{[(A \land (\lnot B \lor C)) \land \lnot C] \lor D \}
\end{align}</math>
The first example is also in [[conjunctive normal form]], the next two are in both [[conjunctive normal form]] and [[disjunctive normal form]], but the last example is in neither.

The following formulae are not in negation normal form:
:<math>\begin{align}
         (A &\to B) \\
  \lnot (A &\lor B) \\
  \lnot (A &\land B) \\
  \lnot (A &\lor \lnot C)
\end{align}</math>

They are however respectively equivalent to the following formulae in negation normal form:
:<math>\begin{align}
  (\lnot A &\lor B) \\
  (\lnot A &\land \lnot B) \\
  (\lnot A &\lor \lnot B) \\
  (\lnot A &\land C)
\end{align}</math>