Re: What is the Result from Invoking this Halt Function?

From: Peter Olcott (olcott_at_worldnet.att.net)
Date: 08/21/04 

Date: Sat, 21 Aug 2004 03:11:41 GMT

"David C. Ullrich" <ullrich@math.okstate.edu> wrote in message news:2imbi0p20o42ubh20bosrciekr2sver8ha@4ax.com...
> On Fri, 20 Aug 2004 02:30:41 GMT, "Peter Olcott"
> <olcott@worldnet.att.net> wrote:

> >> > uh, right. i'll let somone who knows C decide whether this
> >> > works [the fact that there's only a single loop makes me
> >> > doubt it...] the point was to make it as simple to
> >> > understand as possible.
> >>
> >> It's not quite right but it's close.
> >>
> >> int main() { int i,j,k; for(i=j=k=1;--j||k;k=j?i%j?k:k-j:(j=i+=2)); return 0; }
> >>
> >> The main problem with C is that 'int' is a fixed precision, which
> >> means it may not solve the desired problem that it's coded for.
> >> However, the question is still a mildly interesting one;
> >> all I've done is reframed it properly, and now I can compile it. :-)
> >>
> >> >
> >> > does it halt or not?
> >
> >This one would not halt.
>
> ah. how do you -know-? [hint: -proving- it doesn't halt gives
> a solution to a very old problem that nobody knows how to solve.

I know that it does not halt in this case, and the answer is very
easy. I will let you think about it for awhile, and answer on your
next reply, if you haven't yet figured it out by then.

> so you should really explain how you know it doesn't halt, lest
> people assume that you're just guessing. note that since a
> correct answer is going to make you famous, nobody is going to
> believe any weaseling about how you'd just rather not say...]

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