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

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發送短信 : On subgroups of crystallographic Coxeter groups