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

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發送短信 : A Course in Formal Languages, Automata and Groups