發送短信 : Logic functions and equations : examples and exercises

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