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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: comp.theory
Subject: Re: Sequence of sequence, selection and iteration matters
Date: Wed, 10 Jul 2024 10:36:46 +0300
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On 2024-07-09 14:19:59 +0000, olcott said:

> On 7/9/2024 1:22 AM, Mikko wrote:
>> On 2024-07-08 13:04:13 +0000, olcott said:
>>> <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
>>> 
>>>      H can abort its simulation of D and correctly report that D
>>>      specifies a non-halting sequence of configurations.
>>> </MIT Professor Sipser agreed to ONLY these verbatim words 10/13/2022>
>>> 
>>>> Whether a partial simulation of DDD simulates the return depends
>>>> on the simulator.
>>> 
>>> That is false proving that you have insufficient knowledge.
>> 
>> It is true. There are partial simulators that do simulate D(I) to its 
>> termination (if it terminates) and there are simulators that don't.
>> That you cannot imagine something does not mean it can't exist.
>> 
> 
> No pure function x86 emulator HHH can possibly emulate DDD
> to its termination.
> 
> _DDD()
> [00002163] 55         push ebp      ; housekeeping
> [00002164] 8bec       mov ebp,esp   ; housekeeping
> [00002166] 6863210000 push 00002163 ; push DDD
> [0000216b] e853f4ffff call 000015c3 ; call HHH(DDD)
> [00002170] 83c404     add esp,+04
> [00002173] 5d         pop ebp
> [00002174] c3         ret
> Size in bytes:(0018) [00002174]

An emulator can take a shortcut when it has to emulate a call to a
fuction it knows. In case it detects a call to itself it may simply
assume (correctly or incorrectly) that the function returns and
emulate the instructions after the call.

-- 
Mikko