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Proof by…say so

November 5, 2012
The Proof

The professor questions the proof

I do part time teaching and one of the reasons why I enjoy it very much is because I get to learn how young people think. They are very creative and I am fortunate to encounter some of these smart kids in class.

This is the end of the semester and I happen to do some marking for one of the professors in one of the universities where I work. The subject is Theory of Computing and one of the questions the professor asked in exam was…

Q. Prove that the Halting Problem is undecidable.

Here are a couple of proving techniques employed by some of our young people.


Alan Turning says so. Q.E.D.


Our lecture notes state it is true.

Our lecture notes are assumed to be true.

\therefore the Halting Problem is undecidable? Q.E.D.


If a program knew it was going to crash, it would never have run it. Q.E.D.


I mean, how could you fault these answers, they have a point! LOL. 🙂

Do share if you have some examples of this type of proving technique, I will only be too happy to read them.

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