"A man is marooned on an asteroid without food or water and only one day's supply of air in the tanks of his vac suit. If there is an emergency air tank on the asteroid, it contains enough air to last him for two weeks. If there is a flare bomb on the asteroid, then there is an air tank. There is either a dismantled communicator on the asteroid or an emergency water supply, but not both. There is either an emergency food package, or flare bomb, or a single hibernine injection; or there is both an emergency food package and a flare bomb, but no hibernine. If there is an emergency water supply, it contains enough water to last the man four days. If there is a hibernine injection, then there is a dismantled communicator on the asteroid. If there is an emergency food package, there is enough in it to last him for one day, and there is a dismantled communicator, but if they are not both there, then neither is there. If there is emergency air tank, then there is an emergency water supply. "If there is a flare bomb, he can set it off immediately, and rescue will arrive within two days. If there is a dismantled communicator, it will take the man one day to put it together before he can call for help, and rescue will arrive in an additional two days. "If there is an emergency water tank, there is either a single hibernine injection or a food package or both. If there is a hibernine injection, the man can use it to put himself into suspended animation for exactly twenty-four hours, during which time he will need neither air, nor food, nor water. If there is air, or water, or food on the asteroid, or any two of them or all three, the man will use each at the normal rate until it is exhausted, or the man dies, or he is rescued. "Assuming that, without hibernine, the man can live for exactly two days without water, exactly one week without food, and exactly five minutes without air, can he be rescued? If so, how long will it be before he is rescued? If not, what is his maximum survival time? "Does this problem have more than one valid answer? If so, give and explain both. "Or is the problem unsolvable as given? If so, explain why it is unsolvable." Sit around listening to that sort of stuff for very long, and you begin to wish you _were_ out on an uninhabited asteroid somewhere. Problems like that are the sort of thing that any simple-minded computer can solve in a fraction of a second if they're reduced to binary notation first, but poor McGuire had to do his own mathematical interpretations from English, and the things got more complicated as they went along. And McGuire went right on answering them in his calm, matter-of-fact baritone. I remember that particular problem because, while Videnski was reciting it, Brentwood pointed at an oscilloscope plate that had nothing on it but a wide, bright, flickering band of light that wavered a little around the upper and lower edges.