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

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發送短信 : A Singular introduction to commutative algebra