Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Mike Terry <news.dead.person.stones@darjeeling.plus.com>
Newsgroups: comp.theory
Subject: Re: How the requirements that Professor Sipser agreed to are exactly
 met --- WDH
Date: Thu, 15 May 2025 03:08:12 +0100
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On 15/05/2025 01:11, Keith Thompson wrote:
> Ben Bacarisse <ben@bsb.me.uk> writes:
>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>> olcott <polcott333@gmail.com> writes:
>>>> On 5/14/2025 3:51 PM, dbush wrote:
>>>>> On 5/14/2025 11:45 AM, olcott wrote:
>>>>>> On 5/14/2025 6:20 AM, Richard Damon wrote:
>>>>>>>
>>>>>>> And since the DD that HHH is simulating WILL HALT when fully
>>>>>>> simulated (an action that HHH doesn't do)
>>>>>>
>>>>>> *NOT IN THE ACTUAL SPEC*
>>>>>> <MIT Professor Sipser agreed to ONLY these verbatim words 10/13/2022>
>>>>>>       If simulating halt decider H correctly simulates its
>>>>>>       input D until H correctly determines that its simulated D
>>>>>>       would never stop running unless aborted then
>>>>>>
>>>>> That Sipser didn't agree what you think the above means:
>>>>>
>>>>
>>>> If that was actually true then you could provide an
>>>> alternative meaning for the exact words stated above.
>>>>
>>>> I keep challenging you to provide this alternative
>>>> meaning and you dodge because you know that you are
>>>> lying about there being any alternative meaning
>>>> FOR THE EXACT WORDS LISTED ABOVE.
>>>
>>> No alternative meaning is needed, just a correct interpretation of the
>>> words (which appear to be incomplete).
>>>
>>> The quoted sentence is cut off, something that I suspect you didn't
>>> notice.  Here's the full quotation from a previous article:
>>>
>>>>> <Sipser approved abstract>
>>>>> MIT Professor Michael Sipser has agreed that the following verbatim
>>>>> paragraph is correct (he has not agreed to anything else in this
>>>>> paper):
>>>>>
>>>>> If simulating halt decider H correctly simulates its input D until H
>>>>> correctly determines that its simulated D would never stop running
>>>>> unless aborted then H can abort its simulation of D and correctly
>>>>> report that D specifies a non-halting sequence of configurations.
>>>>> </Sipser approved abstract>
>>>
>>> **If** H correctly simulates its input in the manner you claim,
>>> **then** H can correctly report the halting status of D.  (That's a
>>> paraphrase that probably doesn't capture the full meaning; the full
>>> **quotation is above.)
>>>
>>> To put it another way, If H correctly simulated its input in
>>> the manner you claim, then H could correctly report the halting
>>> status of D.
>>>
>>> I'm not surprised that Sipser would agree to that.  The problem is
>>> that it's a conditional statement whose premise is impossible.
>>>
>>> If an equilateral triangle had four sides, then each of its four
>>> vertices would be 90 degrees.  That doesn't actually mean that
>>> there exists an equilateral triangle with four 90-degree vertices,
>>> and in fact no such triangle exists.  Similarly, *if* a general
>>> halt decider existed, then there are a lot of things we could say
>>> about it -- but no general halt decider can exist.
>>
>> It's certainly true that it can be taken to be a purely hypothetical
>> remark, but I suspect PO played a more subtle trick on the professor.
>> Nothing in the quote that PO presented states that D is special in any
>> particular way.  If D is simply "its input" then the statement is simply
>> true of some inputs to H: those that can be determined to be non-halting
>> can be reported as such.  There will be many such inputs if the
>> simulator is clever at detecting certain patterns.
>>
>> But D and H are the names that Sipser uses in his book in his HP proof.
>> Was it made clear that D is not just the name of the input (as the first
>> few words of the quote might suggest) but is in fact one very specific
>> input constructed from H itself?  I don't know, and I doubt we ever
>> will.  If that was made clear, then PO should be saying that Sipser
>> agreed to more than just the quoted words and in that case I'd wager his
>> agreement was based on the hypothetical nature of the quote.
>>
>>> I'm not quite 100% confident in my reasoning here.  I invite any
>>> actual experts in computational theory (not you, PO) to criticize
>>> what I've written.
>>
>> I am no expert, though I did teach this material in a CS degree course
>> for many years.
>>
>> Richard (H) has reminded us about avoiding straw man arguments and to
>> instead address the strongest, clearest version of the point of view we
>> reject.  PO is playing with this idea by constructing straw men to be
>> agreed with!.  He spent years honing a sentence to express his position
>> until is was vague enough that someone important would agree with it.
>>
>> PO should, however, have asked Sipser to agree with an honest and clear
>> statement of his (incorrect) views:
>>
>> (a) That false (non-halting) is the correct result for some inputs that
>> represent halting computations.
>>
>> (b) This is because, in the special case of a putative halt decider that
>> uses simulation, it is correct to report on what /would/ happen were the
>> simulation /not/ aborted.
>>
>> (c) In the specific case where D is constructed from a simulating H in
>> the manner typically found in Halting Theorem proofs, H would then be
>> able to correctly report a result because H can detect that D halts only
>> because H has to stop simulating to report at all.
>>
>> No one would agree to any of this, so PO must hide these points in some
>> sort of waffle or other.  As I say, it took years to move from being
>> relatively clear to being vague enough to trick the professor.  All of
>> (a), (b) and (c) can be found, in varying degrees of clarity, in PO's
>> posts of the last 20 years.
> 
> Fair enough, but what I was trying to do in this instance was
> to focus on the single statement that PO says Sipser agreed to.
> PO complains, correctly or not, that nobody understands or
> ackowledges the statement.  I suggest that perhaps it's actually
> a true statement *in isolation* (very roughly if a working halt
> detector exists then it works as a halt detector), even though it
> does not support PO's wider claims.  I've seen a lot of time and
> bandwidth expended on this one statement (that PO recently hasn't
> even been quoting correctly).
> 
> I do not expect to make any progress in helping PO to see the light.
> I'm just curious about this one statement and the reaction to it.
> I am neither sufficiently qualified nor sufficiently motivated to
> analyze the rest of PO's claims.
> 

I made a post at around 00:36 saying what I suspect Sipser agreed to.  IOW how Sipser expected 
readers (PO included) to interpret the words.

But in the end, PO is making a blatant appeal to authority which should just be rejected.  If PO 
believes his interpretation is a correct statement about simulating halt deciders he doesn't need to 
involve Sipser to try to settle arguments - he can just make his own argument.  Lately he posted, 
admitting he was appealing to authority, and claimed that was "a valid inductive technique" !!!

Yes, it's unpleasant that PO drags Sipser's name into things, and by extension, potentially his 
reputation, but I don't see how to stop that.  I have tried explaining to PO what Sipser's mindset 
would have been, and how he would naturally NOT have taken into account PO's belief that "changing 
the decider code means we have to change the input string to match", but PO's having none of it! 
It's like he thinks Sipser /said the words/, and words have an absolute meaning [which PO knows even 
if nobody else agrees] therefore Sipser agreed with what PO meant QED.  That suggests some basic 
problem with "Theory of Mind" and dealing with other peoples mental states.  ToM develops in 
children around the ages 3-5, so I read.

Maybe the recent suggestion of disengaging from PO when he does this - or at least disengaging from 
that post could work.  Perhaps a single severely trimmed "community response" would be good, along 
the lines

   === Post ignored due to blatant misrepresentation of Sipser's views ===

Or something like...  (But you're unlikely to achieve such a group concensus, and if you did some 
new posters would soon come along...)

Mike.