On Thu, Jun 17, 2021 at 01:04:36AM +0200, Emanuel Berg via Users list for the GNU Emacs text editor wrote:
> Stefan Monnier via Users list for the GNU Emacs text editor wrote:
> 
> >>>> Doing (foo x y) will *never* change "the variable x" -- unless
> >>>> foo is a macro/special form.
> >>> 
> >>> Just to show that you should never say never:
> >>> 
> >>>     (let* ((x 5)
> >>>            (y 6))
> >>>       (cl-flet ((foo (a b) (setq x (+ a b) y (* a b)) (- a b)))
> >>>         (list (foo x y) x y)))
> >>
> >> Hey, that's cheating :-)
> >
> > Impredicativity is borderline, indeed.
> 
> Impredicativity, what's that, recursion?

Kind of. But different [1]

Cheers
[1] https://en.wikipedia.org/wiki/Impredicativity
 - t