Raymond Smullyan. Alice in the country wit (№ 170178)

- Says the one who is out of his mind, man, or some creature that two and two make five? - Alice asked.
- Of course, my child! Because two plus two is not five, the one who is not in his right mind, believes that two and two make five.
And does someone who is not in my mind, that two and two make six? - asked another question, Alice.
- Of course, my child! - replied the Duchess. Since two plus two is not six, the one who is not in his right mind, believes that twice two is six.
But two and two cannot be simultaneously equal to five and six! - exclaimed Alice.
Of course, maybe, ' agreed the Duchess. You and I know that, but one who is not in your mind, about it does not know. And what is the moral of all this?...