Two mathematicians were travelling in an airplane from LA to New York. About an hour into the flight, the pilot announced that they had lost an engine, but not to worry, there were three left. However, instead of 5 hours it would take 7 hours to get to New York. A little later, the pilot again came over the intercom. He announced that a second engine failed, and while they still had two left, it would now take 10 hours to get to New York. Somewhat later, the intercom buzzed again, and the pilot announced that a third engine had died. Never fear, he announced, the plane could fly on a single engine. However, it would now take 18 hours to get to new York. At this point, one mathematician turned to the other and said, "You realize that if we lose that last engine we'll be up here forever!"