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From: olcott <polcott333@gmail.com>
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Subject: =?UTF-8?Q?Re=3A_Analysis_of_Flibble=E2=80=99s_Latest=3A_Detecting_v?=
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On 5/23/2025 10:55 PM, Keith Thompson wrote:
> Ben Bacarisse <ben@bsb.me.uk> writes:
>> Mike Terry <news.dead.person.stones@darjeeling.plus.com> writes:
>>> On 23/05/2025 19:37, Keith Thompson wrote:
>>>> Ben Bacarisse <ben@bsb.me.uk> writes:
>>>>> Mike Terry <news.dead.person.stones@darjeeling.plus.com> writes:
>>>> [...]
>>>>> And the big picture is that this can be done because false is the
>>>>> correct halting decision for some halting computations.  He has said
>>>>> this explicitly (as I have posted before) but he has also explained it
>>>>> in words:
>>>>>
>>>>> | When-so-ever a halt decider correctly determines that its input would
>>>>> | never halt unless forced to halt by this halt decider this halt
>>>>> | decider has made a correct not-halting determination.
>>>> Hmm.  I don't read that the way you do.  Did I miss something?
>>>> It assumes that the input is a non-halting computation ("its input
>>>> would never halt") and asserts that, in certain circumstances,
>>>> his mythical halt decider correctly determines that the input
>>>> is non-halting.
>>>> When his mythical halt decider correctly determines that its input
>>>> doesn't halt, it has made a correct non-halting determination.
>>>> It's just a tautology.
>>>
>>> You're reading it the way most people would, and in the way I said Sipser
>>> would be interpreting the oft-quoted "Sipser quote".  I don't think you've
>>> missed anything particularly.
>>
>> Maybe it makes less sense out of the context it was posted in.  This was
>> when he was being less obtuse.  The computation in question only halts
>> because it is halted by the decider on which it is built.  It is a
>> halting computation, but according to PO it can reported as not halting
>> because of what would happen if it were not halted by the decider from
>> which it is derived.
> 
> I think you're misreading it (or, if you prefer, I have yet to be
> convinced that I'm misreading it).
> 
> | When-so-ever a halt decider correctly determines that its input would
> | never halt unless forced to halt by this halt decider this halt
> | decider has made a correct not-halting determination.
> 
> Call the "halt decider" H, and the input I.  If you perform the
> computation specified by I, it never halts.  olcott's statement
> is that if H correctly determines that I never halts (assume for
> now that that's possible), then H can correctly report that I
> never halts.  This is true, tautological, and uninteresting.
> 
> There is *another* computation, I-simulated-by-H.  This computation
> may halt if H decides to halt it.  But I-simulated-by-H is not I.
> H's alleged job is to determine the halting status of I, not the
> halting status of I-simulated-by-H.
> 
void DDD()
{
   HHH(DDD);
   return;
}

Unless HHH aborts its simulation of DDD it never stops running.

> I think you're saying that H *incorrectly* reports that
> I-simulated-by-H never halts.  My interpretation is that H
> *correctly* reports that I never halts.
> 
> The above is based only on that isolated statement, without reference
> to olcott's other claims.  Moving on to the larger context:
> 
> If a general solution to the halting problem were possible (we
> know it isn't), a simulating halt decider could be one possible
> way to approach it.  It is, I suppose, a tempting idea.  You could
> imagine a simulator that runs a program one step at a time, and
> after each step, reports that it just halted if it has, or performs
> some analysis that attempts to determine that it will never halt.
> If it's able to make that determination, the simulator can halt
> and correctly report that the simulated program never halts.
> 
> If the program runs on a machine with a finite number of states, this
> is actually possible; a repeated state implies that the program is
> in an infinite loop.  The problem is that a Turing machine is not
> limited to a finite number of states (including the state of the
> tape), and such an analysis is not possible in the general case.
> I think olcott thinks it is possible.
> 
>> Subsequent wordings have all been about hiding this.  Just prior to this
>> wording was the even more explicit claim that non-halting is correct
>> because of what "would happen if line 15 were commented out".  It's
>> always been about what would be the correct decision were the
>> computation not what it actually is.
> 
> Sure, I have no doubt that olcott has written contradictory things
> (to the extent that they're clear enough to be contradictory).
> I just don't think he's done is on the case of this specific
> statement.
> 
>>> I suppose Ben quoted PO saying this, because PO /uses/ it to justify that a
>>> particular /halting/ computation will never halt,
>>
>> He may be doing that now, but he used to use this form of words to
>> justify why non-halting is the correct result for some halting
>> computations.  Obviously, to keep people talking he has had to scramble
>> to get away from what he has said in the past without repudiating it.
>> No crank likes admit they were ever wrong.
> 
> Agreed.
> 


-- 
Copyright 2025 Olcott "Talent hits a target no one else can hit; Genius
hits a target no one else can see." Arthur Schopenhauer