For Sebastian to clinch the title in Singapore!!
If he wins;
Fernando has to finish 4th, maximum
Jenson/Webber has to finish 3rd, maximum (If either finishes 2nd though; that means Vettel just has to take 1 point on them again)
If he comes 2nd;
Fernando has to finish 8th, maximum (yeah right; like Nando will finish 8th in Singapore)
Jenson/Webber has to finish 5th, maximum
Hamilton can't win
If he comes 3rd;
Fernando has to finish 9th, maximum
Jenson/Webber has to finish 7th, maximum
If he comes 4th;
Fernando has to finish 10th, maximum
Jenson/Webber has to finish 8th, maximum
If he comes 5th, no title yet.
No matter what happens, Lewis must finish ahead of Sebastian to stay in the championship hunt.