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Ghost Leg (), known in Japan as or in Korea as Sadalitagi (사다리타기, literally "ladder climbing"), is a method of lottery designed to create random pairings between two sets of any number of things, as long as the number of elements in each set is the same. This is often used to distribute things among people, where the number of things distributed is the same as the number of people. For instance, chores or prizes could be assigned fairly and randomly this way. It consists of vertical lines with horizontal lines connecting two adjacent vertical lines scattered randomly along their length; the horizontal lines are called "legs". The number of vertical lines equals the number of people playing, and at the bottom of each line there is an item - a thing that will be paired with a player. The general rule for playing this game is: choose a line on the top, and follow this line downwards. When a horizontal line is encountered, follow it to get to another vertical line and continue downwards. Repeat this procedure until reaching the end of the vertical line. Then the player is given the thing written at the bottom of the line. If the elements written above the Ghost Leg are treated as a sequence, and after the Ghost Leg is used, the same elements are written at the bottom, then the starting sequence has been transformed to another permutation. Hence, Ghost Leg can be treated as a kind of permuting operator. ==Process== As an example, consider assigning roles in a play to actors. # To start with, the two sets are enumerated horizontally across a board. The actors' names would go on top, and the roles on the bottom. Then, vertical lines are drawn connecting each actor with the role directly below it. # The names of the actors and/or roles are then concealed so that people do not know which actor is on which line, or which role is on which line. # Next, each actor adds a leg to the board. Each leg must connect two adjacent vertical lines, and must not touch any other horizontal line. # Once this is done, a path is traced from top of each vertical line to the bottom. As you follow the line down, if you come across a leg, you must follow it to the adjacent vertical line on the left or right, then resume tracing down. You continue until you reach the bottom of a vertical line, and the top item you started from is now paired with the bottom item you ended on. Another process involves creating the ladder beforehand, then concealing it. Then people take turns choosing a path to start from at the top. If no part of the amidakuji is concealed, then it is possible to fix the system so that you are guaranteed to get a certain pairing, thus defeating the idea of random chance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ghost Leg」の詳細全文を読む スポンサード リンク
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