Let us start by consider an ancient position by Erich Lehner, 1887. We will examine how chess engines sometime miss winning opportunities in the endgame. Fortunately, with the judicial application of Chess Assistant 7's multipane analysis features, these situations can be avoided.
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White to move
Let us arrange it on the chessboard. In order to do so, you must select the main menu item Edit\Add New game\ Starting from selected position. Select Clear All item in the diagrams local menu. Then set the position up, click the OK button, and select the multivariation mode of analysis. The program fails to find a way to the win even after prolonged consideration, over 10 minutes (whether tablebases are used or not). It provides an evaluation of approximately +1.75, which corresponds to the approximate material balance, and suggests 1. Kf2? Kh5 2. Kg3 Kh6, or 1. Kf4?? Kh7! 2. Re8 (2. Rg5 Kh6 3. Rg8 Kh7 =) 2... Kg7, resulting in a draw. The white king cannot capture the black f5-pawn, since according to the well known rule a rook cannot stop two connected passed pawns when they reach the third rank, provided the rook does not capture one of the pawns immediately by its move (See the program Comprehensive Chess Endings, or Yuri Averbakh's books).
However, one should remember, that apart from the active plans one more method of winning is available in the endgame, namely, playing for Zugzwang. Zugzwang is a situation where one side has the compulsion to move, but to do so would be disadvantageous. When the weaker side has no active opportunities or any useful moves, or the number of pieces and pawns is reduced and their mobility is restricted, it may create the preconditions for zugzwang. All those traits are present in the given position. The black pawns form a chain protecting each other but they cannot advance. The black king is pressed to the rim of the board; he must:
In order to check the position for zugzwang, let us start the multivariation mode of analysis on two panels:
Observe that the evaluation of the position is much higher when it is Black's turn to move, than it is with Whites turn to move:
Black loses quickly after 1...Kh7 2. Rg5 + , as well as after 1...Kh5 2. Kf4! Kh6 [2Kh4? 3. Rh8#] 3.Kxf5 h2 4. Rh8 +. It is clear now that this is a typical zugzwang position. In order to win, White must pass his turn to Black by losing a tempo. Any piece is capable of losing a tempo except the knight. For example, the king does it by conducting a triangular maneuver. In this case, instead of playing Kf2 (hypotenuse of the e3-e2-f2 triangle), White may play first Ke2, then Kf2 (2 legs of the triangle). Then the white king goes either to e3, or to g3, after having found his black counterpart on h6. The black king then has to move on h5 and White wins by playing Kf4! The black king cannot conduct a reciprocal triangular maneuver; he must move along the h-file.
Thus White wins by playing
1. Ke2!! Kh5
[1... Kh7 2. Rg5 Kh6 3. Rxf5 h2 4. Rf1 g3 5. Kf3+]
2. Kf2 Kh4
[2... f4 3. Rh8+ Kg5 4. Kg1! Kf5 5. Kh2! Ke4 6. Rg8 Kf3 (6... Kf5 7. Rg7! zugzwang f3 8. Kg3+) 7. Rg7! zugzwang Ke2 (7... g3+ 8. Kxh3 Kf2 9. Ra7+) 8. Rxg4 f3 9. Re4+ Kf1 (9... Kd3 10. Rf4 Ke2 11. Kxh3 f2 12. Kg2+) 10. Kg3 f2 (10... h2 11. Rh4+) 11. Rf4+;
2... Kh6 3. Kg3 Kh5 4. Kf4! Kh6 5. Kxf5+]
3. Rg7! zugzwang Kh5
[3... f4 4. Rh7+ Kg5 5. Kg1! Kf5 6. Kh2! Ke4 7. Rg7!+zugzwang;
3... g3+ 4. Rxg3 h2 5. Rg8! h1=Q (5... h1=N+ 6. Kg2+) 6. Rh8+ Kg4 7. Rxh1+]
4. Kg3 Kh6 5. Rg8 Kh5 6. Kf4! Kh6 7. Kxf5+
Let us draw a conclusion. Certain endgames, where the conditions outlined above are present, can be checked for zugzwang using multivariation analysis for both sides. A poor evaluation of the position with the weaker side to move is a clear indication of zugzwang, provided that both analytical modules used are approximately equal in strength (and use approximately equal system resources).