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From: "Fred. Zwarts" <F.Zwarts@HetNet.nl>
Newsgroups: comp.theory
Subject: Re: D correctly simulated by H cannot possibly reach its own line 06
 and halt
Date: Fri, 31 May 2024 17:37:44 +0200
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Op 31.mei.2024 om 16:25 schreef olcott:
> On 5/31/2024 2:50 AM, Fred. Zwarts wrote:
>> Op 31.mei.2024 om 00:01 schreef olcott:
>>> On 5/30/2024 4:54 PM, joes wrote:
>>>> Am Thu, 30 May 2024 09:55:24 -0500 schrieb olcott:
>>>>
>>>>> typedef int (*ptr)();  // ptr is pointer to int function in C
>>>>> 00       int H(ptr p, ptr i);
>>>>> 01       int D(ptr p)
>>>>> 02       {
>>>>> 03         int Halt_Status = H(p, p);
>>>>> 04         if (Halt_Status)
>>>>> 05           HERE: goto HERE;
>>>>> 06         return Halt_Status;
>>>>> 07       }
>>>>> 08
>>>>> 09       int main()
>>>>> 10       {
>>>>> 11         H(D,D);
>>>>> 12         return 0;
>>>>> 13       }
>>>>>
>>>>> The left hand-side are line numbers of correct C code.
>>>>> This code does compile and does conform to c17.
>>>>>
>>>>> Everyone with sufficient knowledge of C can easily determine that D
>>>>> correctly emulated by any *pure function* H (using an x86 emulator)
>>>>> cannot possibly reach its own simulated final state at line 06 and 
>>>>> halt.
>>>> Yeah, of course not, if H doesn’t halt.
>>>>
>>>
>>> To actually understand my words (as in an actual honest dialogue)
>>> you must pay careful attention to every single word. Maybe you
>>> had no idea that *pure functions* must always halt.
>>>
>>> Or maybe you did not know that every computation that never reaches
>>> its own final state *DOES NOT HALT* even if it stops running because
>>> it is no longer simulated. 
>>
>> Since the claim is that H is also a computation, it holds for H, as 
>> well. That means that H *DOES NOT HALT* even if it stops running 
>> because it is no longer simulated.
>>
> 
> *pure function H definitely halts you are confused*
> 

You can assume a unicorn, but that does not make it existent. You can 
assume a simulating H that is a pure function and halts, but that does 
not make them existent. The set of such H is empty.

I stop at your first big mistake so that we can resolve this key
mistake before moving on.

D calls H and if it would be true that H halts, then D would continue 
with line 04. Any competent C programmer will confirm that.
Your claim is that the simulation of D does not reach line 04. That 
means that the simulation of H did not reach its final state. If H halts 
a correct simulation of H halts, too. However, the simulated H does not 
reach its final state, which proves that H has non-halting behaviour.

If not true, show how H halts, i.e. returns from the call from D, but D 
does not continue to line 04.