An engineer and a topologist were locked in the rooms for a day with a can of food but without an opener. At the end of the day, the engineer is in his room and eating from the open can: He threw it against the walls until it cracked open. In the mathematician’s room, the can is still closed but the mathematician has disappeared. Suddenly a voice comes from inside the can: «Damn! I got a sign wrong…»
Pandalilium 