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  _____     ______    ______    ______            
 / ____||  /_   _//  /_____//  /_   _//     ___   
/ //---`'   -| ||-   `____ `    -| ||-     /   || 
\ \\___     _| ||_   /___//     _| ||_    | [] || 
 \_____||  /_____//  `__ `     /_____//    \__ || 
  `----`   `-----`   /_//      `-----`      -|_|| 
                     `-`                     `-`

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發送短信 : Semigroups of transformations with fixed sets