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  _  _     ______    _____     _____             
 | \| ||  /_   _//  /  ___||  |  ___||     ___   
 |  ' ||   -| ||-  | // __    | ||__      /   || 
 | .  ||   _| ||_  | \\_\ ||  | ||__     | [] || 
 |_|\_||  /_____//  \____//   |_____||    \__ || 
 `-` -`   `-----`    `---`    `-----`      -|_|| 
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發送短信 : The compound equation related to the Bessel-Helmholtz equation and the Bessel-Klein-Gordon equation