發送短信 : An introduction to the rational canonical form

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 `____ `   | / \ ||  `-| |,-  | || | ||   \___ \\ 
 /___//    | \_/ ||    | ||   | \\_/ ||   /    // 
 `__ `      \___//     |_||    \____//   /____//  
 /_//       `---`      `-`'     `---`   `-----`   
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