發送短信 : Properties of attractive points in cat(0) spaces

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