So it went, as Princess Nell proceeded from castle to castle, 
inadvertently finding herself at the helm of a full-fledged rebellion against 
King Coyote. Each castle depended on some kind of a programmable system that 
was a little more complicated than the previous one. After the Castle of the 
Water-gates, she came to a castle with a magnificent organ, powered by air 
pressure and controlled by a bewildering grid
of push-rods, which could play music stored on a roll of paper tape with holes 
punched through it. A mysterious dark knight had programmed the organ to play a 
sad, depressing tune, plunging the place into a profound depression so that no 
one worked or even got out of bed. With some playing around, Princess Nell 
established that the behavior of the organ could be simulated by an extremely 
sophisticated arrangement of water-gates, which meant, in turn, that it could 
just as well be reduced to an unfathomably long and complicated Turing machine 
program.