On 10/4/09, Richard Hennessy <rich.hennessy at verizon.net> wrote:
> It would be nice and necessary also that no output label would be created if
> the function returns nothing. So in this case if f(9)
> would get an output label created but f(-9) would get no output label. All
> operations attempting to operate on the return value of
> nothing would also cause a lisp error.
Well, there exists the symbol und which represents "undefined".
Maxima doesn't handle it consistently, however.
E.g. und - und => 0 (oops!)
best
Robert Dodier