\begin{center}\begin{minipage}{15cm}\begin{Verbatim}[frame=single]
> 3/0;
Warning: the given expression is undefined or numerically unstable.
NaN
> (-3)/0;
Warning: the given expression is undefined or numerically unstable.
NaN
> infty/infty;
Warning: the given expression is undefined or numerically unstable.
NaN
> infty + infty;
infty
> infty - infty;
Warning: the given expression is undefined or numerically unstable.
NaN
> f = exp(x) + 5;
> f(NaN);
NaN
> NaN == 5;
false
> NaN == NaN;
false
> NaN != NaN;
true
> X = "Vive la Republique!";
> !(X == X);
false
> X = 5;
> !(X == X);
false
> X = NaN;
> !(X == X);
true
> 
\end{Verbatim}
\end{minipage}\end{center}
