There was a farmer who owed a debt to an ugly old man. The old man proposed that if the farmer's daughter married him, the debt would be eliminated. However, the daughter and farmer did not want this. The old man said the daughter could pick a pebble from a bag - if it was black, she must marry him, and if it was white, she did not have to marry him. However, the daughter noticed he had placed two black pebbles in the bag. Rather than pick a pebble, she dropped the one in her hand on the ground, mixing it with others. She then removed the other pebble from the bag, proving it was black, so the first must have