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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: comp.theory
Subject: Re: Ben Bacarisse fails understand that deciders compute the mapping from inputs
Date: Thu, 29 Aug 2024 11:00:37 +0300
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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?

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?

-- 
Mikko