> A king wishes to find a husband for his daughter, so he sets a difficult
> exam for all the young men in his kingdom. Three men score top marks. In
> order to decide which of the three is most suitable, he sets an
> additional test.
>
> He sits all three in a circle and blindfolds them. He tells them that he
> will place either a red hat or white hat on each of their heads, and
> instructs them to raise their hand if they see a red hat on either of
> the others' heads after he has removed their blindfolds. He places a red
> hat on each of their heads. "The first that can tell me the colour of
> their own hat will marry my daughter." He takes off their blindfolds,
> and they all raise their hands. They sit there for a whole hour before
> finally one of them gets up and says "I have a red hat." How did he know?