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From: olcott <polcott333@gmail.com>
Newsgroups: comp.theory
Subject: Re: D correctly simulated by H cannot possibly reach its own line 06
 and halt
Date: Fri, 31 May 2024 09:25:40 -0500
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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*

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

"...the Turing machine will halt whenever it enters a final state."
Linz(1990:234)

In computer programming, a pure function is a function that has the
following properties:

(1) the function return values are identical for identical arguments
(no variation with local static variables, non-local variables, mutable
reference arguments or input streams), and

(2) the function has no side effects (no mutation of local static
variables, non-local variables, mutable reference arguments or
input/output streams). https://en.wikipedia.org/wiki/Pure_function

DD correctly simulated by pure function HH cannot possibly reach
its own final state at line 06 in any finite number of steps of
correct simulation.

Pure function H reaches its own final state after the finite number
of steps of correct simulation, thus halts.

Linz, Peter 1990. *An Introduction to Formal Languages and Automata*
Lexington/Toronto: D. C. Heath and Company. (317-320)



-- 
Copyright 2024 Olcott "Talent hits a target no one else can hit; Genius
hits a target no one else can see." Arthur Schopenhauer