My question is regarding a mod-deleted answer to: Digital Logic circuit - exam question. In this day and age with modern design methods, it seems to me that a software algorithm used to solve a difficult design problem or prove it is unsolvable, is a valuable tool.

An answer by new user @Ido Kessler presented some source-code that he said ran for 2 hours and returned false. The answer needed a little improvement so I wrote a comment asking that he include a description of the algorithm and his level of confidence that the algorithm was correct and the software bug-free. The question was deleted while I was writing the comment.

Ido Kessler obviously spent some time working on this method of proof and I was intrigued as his method could be adapted to other hardware-design problems and be a useful tool. I therefore feel that this was an important answer and should not have been deleted.

I should note that I had not yet up-voted the answer as I wanted to wait for the improvements I was suggesting, and verification that no one else had a valid solution to the problem (no one did).

What better answer could there be to a problem that is un-solvable than a proof showing that the problem is unsolvable?

Edit: I know that the line for software here is often drawn between embedded (allowed) and PCs (often not allowed); but although the software in the answer was probably intended for a PC, the software was intended to solve a hardware design problem and in my opinion allowances need to be made for that.

Edit2: Here is the link to the restored answer: https://electronics.stackexchange.com/a/330122/25328

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    \$\begingroup\$ Thank you!! I added the code with a lot of explanation. Hopefully, this could be of use. \$\endgroup\$ Commented Sep 21, 2017 at 23:46
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    \$\begingroup\$ Real difficult design problems tend to be more complicated, and this kind of approach (brute force) will take a very very long time (weeks/months/years/millenia) with a realistic problem. \$\endgroup\$
    – BeB00
    Commented Sep 24, 2017 at 10:43

1 Answer 1


I have restored the answer, but it could be improved by the OP.

I'm not sure why, given that the question included the suspicion that there is no solution to the problem as posed, a proof of it would be considered a non-answer. It at least deserves to be discussed.

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    \$\begingroup\$ Thanks! I hope we can get him back. \$\endgroup\$
    – Tut
    Commented Sep 21, 2017 at 13:03

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