4.9 Negation elimination

This one is too simple, but we also have to know it:

$$\begin{fitch*} \par n & \neg\neg A \\ \par \hline \par & A & E$\neg$\ n \par \end{fitch*}$$

So, when we see the negation of the negation of something, we can take off these two following negations.

Remember that the negation of ``this is white'' is not ``this is black'' but ``this is not white''.