Saturday, February 23, 2008

Interesting CTB Error

When using the program Chess Tactics for Beginners, one shouldn't unquestioningly accept their answers. Sometimes there are alternate solutions to the problems that aren't accepted as correct answers. But you should also question their evaluations of variations.

The following problem was interesting. White to draw:

Note: for the following analysis, I'm trying to abide by the Nunn Convention for annotating endgames, hence the extensive use of "!". It's not just me being over-excited. (Technically, some of them might really be "!?", because other moves waste time but don't actually give away the win, but close enough.)

The move 1.Ng1! indeed does lead to a draw, as shown by 1...c1(Q) =. However, the software also gives the following line as a draw: 1...Kf5 2.Ne2 Ke4 3.Kg1 Kd3 4.Kf1 Kd2=. I've checked this with Fritz, and 1...Kf5? actually appears to lose for Black! The main theme appears to be that the white Knight can prevent the c-pawn from promoting (either from e2 or a2, as required) while White queens the h-pawn.

After 1.Ng1!= Kf5?-+ 2.Ne2! Ke4 3.Kg1! Kd3 4.Kf2! (instead of CTB's 4.Kf1?=):

For example, 4...Kd2 5.Kf3! Kd1 6.Nc3+:

It seems clear that Black cannot queen the c-pawn. However, I wasn't ready to trust Fritz yet. I wondered: is it possible that Black can draw the rook-pawn endgame, as I discussed in my previous post? Apparently not. One line continues: 6...Kd2 7.Na2 Ke1 (7...Kd3?! 8.Nb4+. This is a common theme in this, and other knight endgames: some squares such as d3 are "mined" because a king on that square falls victim to a knight fork that wins the offending pawn.) 8.Kg3 Ke2 9.Kxh3 Kf3 10.Kh4 Kf4 11.Kh5 Kf5 12.h4 Kf6 13.Kh6 Kf7 14.h5 Kg8 15.Kg6 Kh8 16.h6 Kg8:

We've followed the drawing procedure for K+RP vs. K, and it looks like Black will draw. However, after 17.Nc1! Kh8 18.Nd3! Kg8 19.h7! Kh8 20.Ne5!:

20...c1=Q 21.Nf7#.

Totally freakin' cool.

Tuesday, February 19, 2008

Another Example of Applying Basic Endgame Knowledge

Here's an example from a recent game where knowledge of a basic endgame helped resolve a more complicated position.

In the case of King and Rook's Pawn vs. King, the defender draws if their king gets in front of the rook pawn. Barring that, if the king can reach the B7 or B8 squares (e.g. f7/f8 vs. an h-pawn), it prevents the attacking king from reaching the key N7/N8 squares (e.g. g7/g8 vs. an h-pawn).

{Aside: although I normally use algebraic notation, the old descriptive notation has one advantage in cases such as this: it doesn't matter if we're talking about white or black queening the pawn, or whether it's the queen's or king's rook pawn.}

For example, in the following position:

Black draws if their king gets to one of the green squares; White wins if their king gets to one of the yellow squares. For example, with Black to move in the above position, 1...Kd7 2.Kg5 Ke7 3.Kg6 Kf8! and Black's king reaches the f8 square and secures a draw:

There are two basic drawing ideas from this position: either get the defending king in front of the rook pawn, or trap the attacking king in front of its pawn.

For example, 4.h4 Kg8! and the king reaches the corner:

White, at best, can stalemate Black (e.g. 5.g5 Kh8 6.h6 Kg8 7.h7+ Kh8 8.Kh6 =).

If White tries to get his own king ahead of the pawn, it can be trapped on the h-file, e.g. after 4.Kh7 Kf7!

As long as White's king is on h7 or h8, preventing Black from reaching g8 and h8, Black keeps his king on the drawing f7/f8 squares. Eventually White will either advance his pawn as far as possible and be stalemated, or he'll try to get his king off of the h-file (e.g. moving to g6), which allows Black to play ...Kg8 and reach the previously described drawing scenario.

There is one exception to this rule that the defender will draw by getting to the B7/B8 square first:

Here, 1.h7! prevents 1...Kg8 and wins.

Studying basic endgames allows you to spot favorable transitions (or avoid unfavorable transitions) to them from more complicated endgames. An example occurred in one of my recent ICC games, where I had White:

If White chooses to capture the d-pawn, does he have to be afraid about Black trading off all the rooks and threatening to queen the h-pawn? {Fritz actually prefers 39.Rg2+!, but we'll let that slide}. No. After 39.Rxd4 Rxd4+ 40.Rxd4 Rxd4+? (Keeping a rook offers the best defensive chances for Black), 41.Kxd4+- Kxf5:

Black has traded down to a lost pawn endgame. On the kingside, we have the standard draw vs. a rook's pawn. However, White has a majority on the queen's side, which wins on its own. The game concluded: 42.b4 (no rush) Kg4 43.Ke4 (or 43.a4--still no need to rush) Kh3 44.Kf3 Kxh2 45.Kf2:

and now the win is clear. The game concluded 45...Kh3 46.a4 Kg4 47.b5 axb5 48.axb5 h4 49.b6 h3 50.b7 h2 51.Kg2 1-0.

If you've avoided studying endgames up to this point, hear me now and believe me later: mastering these basic positions will help your chess.

Reference: Secrets of Pawn Endings, by Muller and Lamprecht

Monday, February 18, 2008

Deceptive Tactic

It took me a few minutes to solve this tactic from "Chess Tactics for Beginners":

The reason is that this looks like it's set up to be the old "windmill" or "see-saw" tactic: rook moves along a rank or file to deliver a discovered check; king moves; rook returns to original square to check. This is normally combined with other threats, such as merely gobbling material with the rook. I was thinking, "well, this is a tactics problem, the answer must involve this tactic" and kept trying to make it work.

Here, rook moves along the 7th rank or the g-file don't accomplish anything. I briefly wondered if the trick was to set up a winning zugzwang after moving the rook, but (for example) 1.Ra7+ Kg8 2.Bg7 can be met by 2...Rf7=.

Then I realized that a safe king move would also put black in zugzwang. Correct is 1.Ka2! Only the black rook can move, and it will be lost to the discovered check (e.g. 1...Ra8+ 2.Ra7+).

However, 1.Kb1 doesn't work, because here the white rook can't block the check after 1...Rf1+, e.g. 2.Ka2 Rf8.

The hardest part of this problem was letting go of my preconception of what the solution must involve, and postponing the "obvious" windmill pattern for one move. Sometimes familiarity with standard tactical motifs can blind you to other tactical possibilities.

Wednesday, February 13, 2008

Interesting Sicilian Tactic

I've set my formula on ICC to play opponents 0-200 points higher than my current rating, and I'm seeing games where the opening resembles something "normal", including a lot more open Sicilians. So far, the Sicilian/Najdorf hybrids seem pretty common, although they seem to leave book quite early. I've been playing Sicilian systems with Bc4, f4, and kingside castling for the most part. I should reread the sections in Soltis' Pawn Structure Chess on the e4-e5 and f4-f5 breaks, since that's a key issue in a lot of my Sicilians.

The following position occurred in a recent ICC game:

I dismissed 14.fxe6, which Fritz discovered, because I thought the exchanges relieved the tension and gave Black a freer game. It turns out that the main line seems to lead to about a pawn advantage for White after 14...Bxe6, but the line isn't very forcing so I forgive myself for not seeing this at the board. What's more interesting is that the alternate recapture 14...fxe6 is a tactical blunder. The reason is the nasty move 15.Nf5!:

There's a few motifs here that I should remember for future games. One is the possibility of a pin on the a2-g8 diagonal allowing a piece to hop into f5. Another is that the bishop on e7 is often insufficiently protected. When lines open up, these factors may come into play.

Here, the knight move is possible because the e5 pawn is pinned. Mate on g7 is threatened, as is the knight fork on e7.

If Black tries to defend by playing 15...Rf7:

White has the simple "removal of the guard" tactic 16. Nxe7+ Rxe7 17. Rxf6, since the g7 pawn is pinned.

Another defensive try is 15...Ng6:

But a removal-of-the-guard/counting tactic gives White the clear advantage: 16. Qxg6! hxg6 17. Nxe7+ Kh7 18. Nxc8. After the knight is recaptured White is a piece up and has a great position to boot.