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From: olcott <polcott333@gmail.com>
Newsgroups: comp.theory
Subject: Indirect Reference Changes the Behavior of DDD() relative to DDD
 emulated by HHH
Date: Thu, 29 Aug 2024 09:04:05 -0500
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On 8/29/2024 3:00 AM, Mikko wrote:
> On 2024-08-28 11:46:58 +0000, olcott said:
> 
>> On 8/28/2024 2:33 AM, Mikko wrote:
>>> On 2024-08-27 13:04:26 +0000, olcott said:
>>>
>>>> On 8/27/2024 12:45 AM, joes wrote:
>>>>> Am Mon, 26 Aug 2024 18:03:41 -0500 schrieb olcott:
>>>>>> On 8/26/2024 7:42 AM, Ben Bacarisse wrote:
>>>>>>> Mike Terry <news.dead.person.stones@darjeeling.plus.com> writes:
>>>>>>>> On 23/08/2024 22:07, Ben Bacarisse wrote:
>>>>>
>>>>>>>>> We don't really know what context Sipser was given.  I got in 
>>>>>>>>> touch
>>>>>>>>> at the time so I do know he had enough context to know that PO's
>>>>>>>>> ideas were "wacky" and that had agreed to what he considered a 
>>>>>>>>> "minor
>>>>>>>>> remark". Since PO considers his words finely crafted and key to 
>>>>>>>>> his
>>>>>>>>> so-called work I think it's clear that Sipser did not take the 
>>>>>>>>> "minor
>>>>>>>>> remark" he agreed to to mean what PO takes it to mean!  My own 
>>>>>>>>> take
>>>>>>>>> if that he (Sipser) read it as a general remark about how to
>>>>>>>>> determine some cases, i.e. that D names an input that H can 
>>>>>>>>> partially
>>>>>>>>> simulate to determine it's halting or otherwise.  We all know or
>>>>>>>>> could construct some such cases.
>>>>>>>>
>>>>>>>> Exactly my reading.  It makes Sipser's agreement natural, 
>>>>>>>> because it
>>>>>>>> is both correct [with sensible interpretation of terms], and 
>>>>>>>> moreover
>>>>>>>> describes an obvious strategy that a partial decider might use that
>>>>>>>> can decide halting for some specific cases.  No need for Sipser 
>>>>>>>> to be
>>>>>>>> deceptive or misleading here, when the truth suffices.  (In 
>>>>>>>> particular
>>>>>>>> no need to employ "tricksy" vacuous truth get out clauses just 
>>>>>>>> to get
>>>>>>>> PO off his back as some have suggested.)
>>>>>>>
>>>>>>> Yes, and it fits with his thinking it a "trivial remark".
>>>>>
>>>>>>> That aside, it's such an odd way to present an argument: "I 
>>>>>>> managed to
>>>>>>> trick X into saying 'yes' to something vague".  In any reasonable
>>>>>>> collegiate exchange you'd go back and check: "So even when D is
>>>>>>> constructed from H, H can return based on what /would/ happen if 
>>>>>>> H did
>>>>>>> not stop simulating so that H(D,D) == false is correct even 
>>>>>>> though D(D)
>>>>>>> halts?".  Just imagine what Sipser would say to that!
>>>>> Is this an accurate phrasing, pete?
>>>>
>>>> Deciders never compute the mapping of the computation
>>>> that they themselves are contained within.
>>>
>>> Why not? A decider always either accepts or rejects its input.
>>
>> The computation that they themselves are contained within cannot
>> possibly be an input.
> 
> What would prevent that if the input language permits computations?
> 

When a TM takes its own machine description as input
this is not always that same behavior as the direct
execution of the machine. It is not the same because
it is one level of indirect reference away.

*How one level of indirect reference changes the answer*
Does this sentence:
"This sentence is not true"
have a truth value? No, it is not a truth bearer.

Does this sentence:
This sentence is not true: "This sentence is not true"
have a truth value? Yes it is true.

> For example, every computation can be given to an UTM. That computation
> may involve a decider X that uses the same input language. What
> What prevents giving X the same input as the UTM was given?
> 
One level of indirect reference away from the
computation itself can have different behavior

The direct execution of DDD() has the benefit of
HHH having already aborted its emulation of DDD.

DDD emulated by HHH does not have this same benefit.

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