發送短信 : A coupled system of difference equations

 _    _      ___                 ___     ______   
| |  | ||   / _ \\      ___     / _ \\  |      \\ 
| |/\| ||  | / \ ||    /   ||  / //\ \\ |  --  // 
|  /\  ||  | \_/ ||   | [] || |  ___  |||  --  \\ 
|_// \_||   \___//     \__ || |_||  |_|||______// 
`-`   `-`   `---`       -|_|| `-`   `-` `------`  
                         `-`