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

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發送短信 : Two classes of topological acoustic crystals