4.9 Negation elimination

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

n & \neg\neg A \\
& A & E$\neg$\ n
\end{fitch*} \end{displaymath}

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''.

Daniel Clemente Laboreo 2005-05-17