By Robert Waltz

THE MEN

1. Has Rafael Nadal clinched the year-end No. 1 or could Roger Federer still catch him?

To clinch the year-end No. 1, almost all Nadal has to do is show up.

To steal No. 1 back, by contrast, Federer has to win Madrid, Paris and the Masters Cup in Shanghai, and hope that Nadal doesn't reach another final this year. If Federer pulls out of any of those three events, his chances would be over.

Concretely, Nadal has earned 1,720 more ranking points than Federer this year. Winning Madrid, Paris and Shanghai would give Federer a maximum of 1,750 points -- if he wins Basel in between, he would get a total of 2,000 points. But if Nadal earns more than 280 points during the fall, he'll end the year as No.1 no matter what Federer does.

2. Is Novak Djokovic completely out of the year-end No. 1 race?

Effectively, yes, unless he somehow wins a title every week and Nadal doesn't play at all. But the Serb is only scheduled to play Madrid, Paris and Shanghai. Unless he adds an event to his schedule, he cannot catch Nadal.

3. Is Federer at least safe at No. 2?

No, and Djokovic is closer than you might think. Looking at this season's results, they're separated by just 110 points at the moment -- slightly less than the equivalent of a quarterfinal in Madrid or Paris.

To end the year as No. 2, Federer must more or less match Djokovic's results this fall. If he pulls out of an event, he'll likely be playing catch up.

4. Will Federer have a chance to get to No. 1 in Melbourne?

Much depends on how Nadal does during the fall. If Nadal does well in Madrid, Paris and Shanghai -- winning one and reaching the finals of the other two, for example -- he'll secure the No. 1 ranking through the Australian Open. But if Nadal does what he did last year -- Madrid quarterfinal, Paris final, Shanghai semifinal -- then Federer would have a chance.

But it still won't be easy. For his part, Federer would have to at least win Basel, Paris and Shanghai. If Federer's goal is to return to No. 1 in Melbourne, Federer would almost certainly have to play in, and do well at, all of the fall tournaments.

5. Is Djokovic more likely to go up in the rankings or down?

He has a chance to move up during the rest of this year, but could drop early next year if he doesn't defend his Australian Open title.

The Serb did little during the fall last year and, as mentioned, he could overtake Federer if he can outperform him over the next few weeks.

But after a fast start in Melbourne and Indian Wells early this season, Djokovic has accumulated points only slightly faster than Andy Murray. The gap between them starting from the Australian Open is about one Slam's worth. So Djokovic also needs to do better than Murray this fall if he wants to be sure of staying No. 3 after Melbourne.

THE WOMEN

1. How many players have a chance of ending the year at No. 1?

Theoretically, Jelena Jankovic, Serena Williams, Dinara Safina, Elena Dementieva, Ana Ivanovic, Svetlana Kuznetsova, Venus Williams, and Vera Zvonareva all have chances. Maria Sharapova would also be on the list if she were playing.

2. Who has a good chance?

Jankovic, Serena, and Safina.

Kuznetsova, Venus, and Zvonareva don't have enough events scheduled to have a chance of overtaking the top three. Either of them would need titles at Moscow, Zurich and Doha. Ivanovic is quite far back, and her recent results aren't cause for optimism. Dementieva is only a little better off, though she is in better form.

But Ivanovic, Dementieva, and Kuznetsova do have a chance of moving up to No. 3 if any of them has a good fall season.

3. What does Jankovic have to do to clinch?

Win the year-end championships in Doha, or win any other title plus one other good result. Beyond that, it depends on how others do. Taking each player's best 17 scores so far -- i.e. her guaranteed minimum points total at the end of the season  -- Jankovic has about a 400-point lead on the competition.

4. What does Serena have to do?

Because she's not playing until Doha, Serena has to win the year-end championships and hope that Jankovic earns fewer than 350 points at Moscow, Zurich, and Doha. That's a very tall order -- in round numbers, all Jankovic needs is three semifinals to block her.

5. What does Safina have to do?

Safina is roughly tied with Serena, and she will be playing Moscow, so she currently looks like the main threat to Jankovic. A title at Moscow would effectively put her even with Jankovic, meaning that whoever does better at Doha would be the year-end No. 1.