發送短信 : A note on the symmetrization method of operator formation

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