One day Isidra went to market to buy new clothes. First she tried on a pair of trousers. She didn't like the trousers, so she gave them back to the shopkeeper. Then she tried a robe which had the same price as the trousers. Isidra was pleased with the robe, and she left the shop. Before she climbed on her donkey to ride home, the shopkeeper and the shop-assistant ran out.

"You didn't pay for the robe!" said the shopkeeper.

"But I gave you the trousers in exchange for the robe, didn't I?" replied Isidra.

"Yes, but you didn't pay for the trousers, either!" said the shopkeeper.

"But I didn't buy the trousers," replied Isidra. "I am not so stupid as to pay for something which I never bought."