09 June 2013

Understanding Defensive Resources

Problem 147 in level 3 of Chess Quest gave me some trouble this morning. Spotting the sacrifice to open the h-file took me a few seconds, but after that the problem became more complicated. In retrospect, the ability of the knight on e5 to cover h8 from g6 should have been obvious.

White to move

The main solution in the Chess Quest app is 1.Nxh5 gxh5 2.Nd5

White's second move accomplishes several things: discovered attack on the troublesome knight, interference along the a8-h1 diagonal, and attack of the Black queen.

Chess Quest has two responses for Black.

a) 2...Ng4 is the main line

b) 2...exd5 is the alternate line

Neither of these moves are the top choices of the engines I employed in my effort to comprehend the problem after multiple tries were necessary to solve it on the iPad.

Houdini 1.5 played 2...Ne3.

White to move

I first tried 3.Nxc7 and lost my way after 3...Nxd1 4.Bd4 Ng6 5.Nxe8 Rc1 6.Bf1 e5 7.Bxb6 Rc3

White to move

Taking the queen maintains an advantage, but Black is able to complicate matters enough that my humanity reveals itself through errors in battle with the silicon beast.

I fared better against the machine with 3.Rxh5 Ng6 4.Rh6 e5 5.Nxc7 Rxc7 6.Rxg6+ fxg6 7.Qxe3

Black to move

With Black's pesky knights gone and the queen removed at the opportune time, White has a clear advantage and Black has limited counterplay.

Chess Quest's main line continues 2...Ng4 and White must stop the threatened fork. 3.Rf1 exd5.

Black has other moves that delay checkmate more moves. These are spite threats that give away major pieces. In terms of the problem themes--h-file penetration, and Black's efforts to control h8--3...exd5 is almost as good as anything else. Perhaps, however, 3...Ne5 might have been entered into the sequence by the creator of the problem.* White must then play 4.Bxe5 before proceeding along the h-file.

The main line concludes 4.Rxh5 Bg7 5.Rh7 and White is winning.

The alternate line tests the solver's understanding of the importantance of the knight on e5.

2...exd4 3.Bxe5 (3.Rxh5 Ng6 leads to a winning position for Black) 3...Rxe5 4.Rxh5 h-file penetration is now or never 4...Bg7 5.Rh7 Kf8

White to move
After 5...Kf8
 5...Kf8 is a subpar move. Black puts up more resistance with 5...Rxg5.

Unfortunately, Chess Quest rejects 6.Rh8+ in favor of 6.Rxg7, while both moves lead to checkmate on the following move. After 6.Rxg7 Ke8, Chess Quest accepts only 7.Qh8+. According to Stockfish 2.3.1, this move is the ninth best. 7.Rg8# is obviously best. 7.exd5 leads to the second fastest checkmate.

After 7.Qh8+ Chess Quest's line continues 7...Kd7 8.Rxf7 Ke6 and now White has three routes to checkmate in five moves. Chess Quest accepts only 9.Bh3+.

Chess Quest also has 8...Kc6 9.Rxc7+ (exd5+ is a better move, but not accepted by the app).

The problem is well-designed for highlighting defensive resources in a battle against an h-file battery, and for understanding that checkmating the king takes precedence over gaining material. Alas, the errors in the alternate solution confuse this message.

*Chess Quest "About" claims the GM Leonid Yudasin created the problems.

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