An engineer, a physicist and a mathematician were traveling together. One night three fires broke out in each of their hotel rooms. The engineer got a bucket of water and threw it all over the place including the bed which was not on fire, but he did put out the fire. The physicist drew a square box around the fire, filled a glass of water and poured the water one the square's line. The fire burned out to the line and went out. The mathematician stared at the fire, ran into the bathroom, turned on the water, looked at it, touched it, ran back and looked at the fire, again ran into the bathroom, turned on the water, looked at it, touched it, then he came out to the hallway and announced "A solution exists. QED."