發送短信 : Solid angles and Seifert hypersurfaces

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