On 10/20/2021 8:37 PM, Ben Bacarisse wrote:
> olcott <No...@NoWhere.com> writes:
>
>>> This notation is hopeless in ASCII. Using the notation that has evolved
>>> in these threads (not my preferred one, but I don't want to complicate
>>> matters any more) Linz writes:
>>> Ĥ.q0 <M> ⊢* Ĥ.qx <M> <M> ⊢* y1 Ĥ.qn y2
>>> if M applied to <M> does not halt.
>>> And with these changes in notation you seem to be saying
>>>
>>>> Linz cannot be correctly referring to Ĥ applied to <M> because there
>>>> is no halt decider at q0.
>>> Yes, there is no halt decider at Ĥ.q0, but he is correctly referring to
>>> what Ĥ applied to <M> should do: Ĥ applied to <M> should transition to
>>> Ĥ.qn if (and only if) M (the TM encoded in the string input) applied to
>>> <M> (that exactly same string input) does not halt.
>>> Your next point helps explain how he comes to say this about Ĥ.
>>>
>>>> Linz can only be referring to Ĥ.qx <M> <M> the machine of the first
>>>> <M> being applied to the machine description of the second <M>.
>>>
>>> The annotation dose not specifically refer to what this sub-computation
>>> does. It simply gives the condition under which Ĥ will transition from
>>> Ĥ.q0 to Ĥ.qn.
>>
>> If a simulating halt decider H correctly determines that the
>> simulation of its input <M> applied to <M> never reaches its final
>> state whether or not this simulating halt decider aborts the
>> simulation of this input then this simulating halt decider does
>> correctly decide that this input never halts NO MATTER WHAT ELSE.
>
> This is not what Linz is saying.
Of course this is not what Linz is saying. Linz is still under the
misconception that Ĥ.q0 applied to <Ĥ> <Ĥ> would not correctly
transition to H.qn.
> If I can help with any further
> explanation, I'm happy to have a go but you need to stop repeating what
> you are saying and try to focus on what Linz is saying. Once you get
> what he is saying you will see that you can say anything you like about
> a subclass (those that "simulate") of the empty class of TMs (the halt
> deciders) that Linz is talking about. Atatements about no TMs are
> vacuously true (or irrelevant -- take your pick).
>
>> Anything and everything that is not input to this halt decider is 100%
>> totally irrelevant.
>
> Technically, there is no halt decider in the TM you are talking about,
> but that's a detail and you don't do details. Did you follow what I
> wrote about how the string input to the almost-decider at Ĥ.qx is
> entirely why Linz's annotation is correct? Here it is:
>
>>> But you are correct in that the annotation /derives/ from what we know
>>> about the modified copy of H embedded at Ĥ.qx. We know that
>>> H.q0 <M> s ⊢* y1 H.qn y2
>>> if M applied to s does not halt.
>>> and since the TM at Ĥ.qx is (in this regard at least) exactly like H we
>>> know that
>>> Ĥ.qx <M> <M> ⊢* y1 Ĥ.qn y2
>>> if M applied to <M> does not halt.
>>> Now, because
>>> Ĥ.q0 s ⊢* Ĥ.qx s s
>>> for /any/ string s, we know, specifically, that
>>> Ĥ.q0 <M> ⊢* Ĥ.qx <M> <M> ⊢* y1 Ĥ.qn y2
>>> if M applied to <M> does not halt.
>>> Can you now see where this correctly annotated line comes from? Can I
>>> explain any part of this some other way to make it clearer?
>
> I suspect you simply didn't read it since I am agreeing with you about
> the central role of the Ĥ.qx <M> <M> part in explaining why Linz is
> correct.
>
So you are agreeing that when Ĥ.qx simulates <Ĥ> applied to <Ĥ> and
correctly determines that the simulated <Ĥ> never reaches its final
state (whether or not Ĥ.qx stops simulating <Ĥ>) then Ĥ.qx correctly
aborts this simulation and transitions to qn ???
If we have to go over this same point thousands of times I will.
This one point proves that I have shown how to defeat the halting theorem.
Let's standardize on this notation so that new people will
be able to more easily see how it relates to the Linz text.
⟨Ĥ⟩ indicates the Turing machine description of Ĥ.
The machine at Ĥq0 transitions to Ĥqn if the simulation of ⟨Ĥ⟩ applied
to ⟨Ĥ⟩ would never reach its final state whether or not this simulation
is aborted.
// Adapted from bottom of page 319 (definition of Ĥ)
q0 ⟨Ĥ⟩ ⊢* Ĥq0 ⟨Ĥ⟩ ⟨Ĥ⟩ ⊢* Ĥ∞
If the simulated input to Ĥq0 ⟨Ĥ⟩ applied to ⟨Ĥ⟩ halts
q0 ⟨Ĥ⟩ ⊢* Ĥq0 ⟨Ĥ⟩ ⟨Ĥ⟩ ⊢* Ĥqn
If the simulated input to Ĥq0 ⟨Ĥ⟩ applied to ⟨Ĥ⟩ does not halt
https://www.liarparadox.org/Peter_Linz_HP(Pages_315-320).pdf
All dialogue must be either agreeing with the above or pointing out
errors in the above. Changing the subject will generally be ignored
except that it will be pointed out as a dishonest dodge away from the
point.