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On 21/05/2025 21:28, olcott wrote:Show an actual input to HHH that actually doesOn 5/21/2025 3:13 PM, Richard Heathfield wrote:<snip>On 21/05/2025 20:28, olcott wrote:
Correct. We have derived an impossible consequence of our assumption, thus proving that the assumption is false.>I have only been talking about the ACTUAL>
conventional proof of the halting problem.
The ACTUAL conventional proof of the Halting Problem goes something like this:
>
1) assume that it is possible to devise an algorithm that can determine in finitely many steps ascertain whether an arbitrary program applied to arbitrary data does or does not stop.
>
2) given such an algorithm, imagine incorporating it into a program that ascertains whether a supplied program with supplied data halts, loops if it does, and halts if it doesn't.
>
This step is impossible.
It only seemed possibleNo. It never seemed possible. It always seemed like the impossible contradiction that it is.
because no one everWhy would they? One would have to be pretty stupid to try.
tried to completely encode every detail.
This screwy mistake came aboutIt's not screwy, and it's not a mistake. It's a proof that there is at least one thing which we'd like a computer to be able to do but which it will never be able to do.
Like you said, it's impossible. QED.
because fools thoughtWhat your halt decider reports on is entirely up to you, but thanks to Turing we know that it will not be able to act as a /universal/ termination analyser that always gets the answer right regardless of the input.
that a halt decider H is supposed to report on the behavior
of the program that itself is contained within rather
than the behavior that its actual input actually specifies.
Sometimes? Sure. bool decide(whatever){return true;} will get it right sometimes. But for some inputs your decider will get it wrong.
int main()
{
DDD(); // No HHH can report on the behavior of its caller.
}
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