發送短信 : An introduction to the rational canonical form

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