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 __   _     _____     ______   _    _    _    _   
| || | ||  |  ___||  /_____// | || | || | || | || 
| '--' ||  | ||__    `____ `  | || | || | || | || 
| .--. ||  | ||__    /___//   | \\_/ || | \\_/ || 
|_|| |_||  |_____||  `__ `     \____//   \____//  
`-`  `-`   `-----`   /_//       `---`     `---`   
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發送短信 : A Singular introduction to commutative algebra