A crocodile steals a child. When the mother complains, the crocodile makes the following proposal:
"I'll return the child if you guess if I will return it or not."
The mother answers: "You will not return my child."
What should the crocodile do? If he returns the child, it goes into contradiction because the mother made a mistake. But if the crocodile does not return it, the same happens because the mother answered correctly.