Tower of Hanoi

n. A puzzle used in studies of problem solving in which three or more doughnut-shaped disks are stacked on any of three posts and the subject is required to move the disks one at a time from wherever they begin to one post, with the largest disk on the bottom and the smallest on top, without ever placing a larger disk on top of a smaller disk. Additional disks and posts may be added in order to make the task more difficult.