return in loop for ?

[Steven D'Aprano]

On Thu, 24 Nov 2005 12:51:34 +0000, Duncan Booth wrote:

> Steven D'Aprano wrote:
> 
>>> While outwardly they apear to offer a technique for making software
>>> more reliable there are two shortcomings I'm leery of. First, no
>>> verification program can verify itself; 
>> 
>> That's not a problem if there exists a verification program A which
>> can't verify itself but can verify program B, which in turn also can't
>> verify itself but will verify program A.
>> 
> That is logically equivalent to the first case, so it doesn't get you 
> anywhere. (Just combine A and B into a single program which invokes A 
> unless the input is A when it invokes B instead.)

Then there you go, there is a single program which can verify itself.

I think you are confabulating the impossibility of any program which can
verify ALL programs (including itself) with the impossibility of a program
verifying itself. Programs which operate on their own source code do not
violate the Halting Problem. Neither do programs which verify some
subset of the set of all possibly programs.


-- 
Steven.