Well, I've finally decided on 21.f5.  Although I favored 21.Rh6 at first, I started hearing this Obewan-like voice in my head saying:

"Trust your feelings.  Use the f-pawn, Ostap."

(or maybe it was an MNb-like voice!)

And suddenly it dawned on me: f is for force!

1.e4 e6 2.d4 d5 3.Nc3 Nf6 4.e5 Nfd7 5.f4 c5 6.Nf3 Nc6 7.Be3 cxd4 8.Nxd4 Bc5 9.Qd2 0-0 10.0-0-0 a6 11.Nb3 Bb4 12.Bd3 b5 13.g4 Bb7 14.Rhg1 Na5 15.Rg3 Nc4 16.Qe1 Qh4 17.Bd4 Rfc8 18.Qf1 Qe7 19.Kb1 g6 20.Rh3 Bc6 21.f5




As far as Black's responses go, I've looked mainly at the two captures 21...Ncxe5 and 21...Ndxe5.  It appears to me that the capturing with the c4-knight might be Black's best try.  I also looked at 21...Qg5 focusing on 22.Qe2 Bf8, which had me a bit worried for a while.  I now think White should be OK after Bxc4 (either right away or perhaps after a useful waiting move).  White can probably gain time to improve his pieces by forcing Black's queen to retreat from g5 (Be3 followed by Nd4 is one attractive possibility).

Overall I would still call this position unclear (too much going on to calculate all possibilities), but I like White's chances for seizing the initiative on the kingside.

After 21.f5 Qg5 22.Qe2, I looked at 22...Ncxe5 and White definitely has nothing to fear here:

Instead of playing 23.fxe6 (which also has it's points), White can just capture the knight: 23.Bxe5 Nxe5 24.Qxe5

24...Qxg4 loses to 25.fxg6! Qxh3 26.gxh7+ Kf8 27.h8Q+

Alternatively, 24…Bxc3 25.bxc3

And here 25...Qxg4 loses to the same move: 26.fxg6! 

Neither rook capture works:
26...Qxd1+ 27.Kb2 h5 28.Rxh5 and wins.
26...Qxh3 27.gxh7+ Kf8 28.h8Q+ and wins.

So Black has nothing better than 26...fxg6 which loses to 27.Bxg6!

Most other moves can be answered by something simple like 26.Qg3 and Black is just a piece down.

So, after 21.f5 Qg5 22.Qe2 I think Black's best try might be 22...Bf8.  This is the move I'm focusing on at the moment, anyway.

21...Qg5 22.Qe2 Ncxe5 23.fxe6 fxe6 24.Re3 Nxd3 25.cxd3 and Black has a little problem with the black squares.

Ostap,

Please take all the time you need to make your move. I'm rather busy at the moment, so I'm in no hurry whatsoever about your making your move.

Best regards,
WAS

MNb wrote on 01/31/07 at 01:33:44:

After 21.f5 Ncxe5 22.Re1, 22...Bd6 looks like a good defense.  This seems to be another example where 21...Ncxe5 is the preferred capture.  White's prospects after 21.f5 Ndxe5 22.Re1 Bd6 look quite good after 23.Bxc4.

Quote:

After 21.Rh6 Qf8 22.Qh3 Qg7 23.Nd2 Bf8, 24.g5 seems to offer White good prospects.  In the line 21.Rh6 Qf8 22.Qh3 Qg7 23.g5 (a move which may be better than it looks) 23...a5, I have 24.Nd2 and White seems to do well after 24...Bxc3, 24...Bc5 or 24...Be7.

Quote:

As long as I can work out a good response to 21.f5 Ncxe5 22.Re1 Bd6 (and I think I will based on either 23.fxe6 or 23.fxg6), then 21.f5 remains a very likely choice.

MNb wrote on 01/30/07 at 20:35:15:

Looks like I misinterpretted your last post a bit.  Sorry about that – sometimes I can get carried away in my enthusiasm.  I hope you understand that I was just trying to engage you in discussion – not to tear down your suggestions of otherwise put you on the spot.   

BTW, you are correct about having steered my thoughts toward 21.f5.  Prior to your post, I'd practically decided that 21.Rh6 was the only move really worth considering.  Thanks for this.

Dear Ostap,

let me make one thing clear once and for all. The lines I produce are more or less wild guesses. I do not pretend to have found optimal play for both sides at all; for something like that I by far do not spend enough time. I am a pure kibitzer: what about this, what about that?
1. When I asked, have you looked at 23...Bf8, I meant after every random White move you might have had in mind.
2. If you don't know the logic behind moves like 23.Nd2 and 23.g5, how do you expect me to know the logic behind the moves I propose? I intuitively just feel, that White must strive for f4-f5 - so I might be dead wrong, as my intuition quite often fails me.
So I simply can't answer your questions. I only hope to steer your thoughts in a path worth trodding and bring up a few suggestions, you had not noticed yet. And I am happy that I have succeeded, as you have paid more attention to 21.f5 than you did initially. 

And I simply never have looked at 21.Rh6 Qf8 22.Qh3 Qg7 23.Re1 a5. May I bring into your attention, that it was you, who initially thought so high of f4-f5-f6, forcing the black queen to h8?

It is the same with 21.f5 Ndxe5. It is very possible, that 22.Re1 is stronger than 22.Qf4.
In full conscience that you see and analyse at least ten times as much as me,

MNb

With regards to MNb's post: 
Have you looked at 27...Qxd6 28.Rxd6 Rf1+ 29.Kd2 Kg8 30.Rxa6 Rf2+ with an active rook and 24...Kxf8 25.Qe4 Bg5+ 26.Kb1 Kg8 ?
The keyword for Black's play is activity.

Instead of (20...Rad8 21.Qd4 Qc6 22.Bxe6+ Qxe6 23.Nxd5 fxe5) 24.Rxf8+ Rxf8 25.Nxe7+ Qxe7, taking the bishop on e7 first, forces the position after the 25th move. That is, after 24.Nxe7+ Qxe7 25.Rxf8+ then black has to play Rxf8, ending up at the same position. 

And thanks for the suggestion, but I don't think 27...Qxd6 28.Rxd6 Rf1+ 29.Kd2 Kg8 30.Rxa6 Rf2+ quite works. For instance, after 31.Kd3 Rxg2 32.Rb6 Kf7 33.Rb5 Kf6 34.a4 Rxh2 35.a5 white's three connected passed pawns and better piece coordination look winning to me.