Effect of Tablebases On Endgame Theory
Endgame tablebases have made some minor corrections to historical endgame analysis, but they have made some more significant changes to endgame theory too. (The fifty-move rule is not taken into account in these studies.) Major changes to endgame theory as a result of tablebases include (Müller & Lamprecht 2001:8,400–406):
- Queen versus rook (see Philidor position#Queen versus rook). There are two changes here enabling the rook to put up a better defense, but the queen still wins. (a) People usually opt for a second-rank defense with the rook on the second rank and the king behind it (or symmetrical positions on the other edges of the board). Tablebases show that a third-rank defense takes a while to breach, which is difficult for a human to do. (b) People had assumed that the rook needs to stay as close to the king for as long as possible, but tablebases show that it is best to move the rook away from the king at some earlier point (Nunn 2002:49ff).
- Queen and pawn versus queen. Tablebases have shown that this can be won in many more positions than was thought, but the logic of the moves is presently beyond human understanding (Nunn 1995:265).
- Queen versus two bishops. This was thought to be a draw due to the existence of a drawing fortress position, but the queen can win most of the time by preventing the bishops from getting to the fortress. However, it can take up to 71 moves to force a win (Nunn 2002:290ff).
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| 8 | 8 | ||||||||
| 7 | 7 | ||||||||
| 6 | 6 | ||||||||
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| 2 | 2 | ||||||||
| 1 | 1 | ||||||||
| a | b | c | d | e | f | g | h |
- Queen versus two knights. This was thought to be a draw and generally it is, but the queen has more winning positions than was previously thought. Also, many analysts gave a position (see diagram) that they thought was a draw but it is actually a win for the queen (Nunn 2002:300ff). In the diagram, White checkmates in 43 moves, starting with 1. Qc7 (the only winning move). Note that Nunn says "The general result is undoubtedly a draw, but there are many losing positions, some of them very lengthy." On the other hand, Batsford Chess Endings states that 89.7 percent of the starting positions are wins for the queen (Speelman, Tisdall & Wade 1993:7). However, these percentages can be misleading, and most "general results" are based on the analysis of grandmasters using the tablebase data (Müller & Lamprecht 2001:406), (Nunn 2002:324). For instance, although nearly 90 percent of all of these positions are wins for the queen, it is generally a draw if the king is not separated from the knights and they are on reasonable squares (Müller & Lamprecht 2001:339).
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| 8 | 8 | ||||||||
| 7 | 7 | ||||||||
| 6 | 6 | ||||||||
| 5 | 5 | ||||||||
| 4 | 4 | ||||||||
| 3 | 3 | ||||||||
| 2 | 2 | ||||||||
| 1 | 1 | ||||||||
| a | b | c | d | e | f | g | h |
- Two bishops versus a knight. This was thought to be a draw but the bishops generally win. However, it takes up to 66 moves. The position in the diagram was thought to be a draw for over one hundred years, but tablebases show that White wins in 45 moves. All of the long wins go through this type of semi-fortress position. It takes several moves to force Black out of the temporary fortress in the corner; then precise play with the bishops prevents Black from forming the temporary fortress in another corner (Nunn 1995:265ff). Before computer analysis, Speelman listed this position as unresolved, but "probably a draw" (Speelman 1981:109).
- Queen and bishop versus two rooks. This was thought to be a draw but the queen and bishop usually win. It takes up to 84 moves (Nunn 2002:367ff).
- Rook and bishop versus bishop and knight, bishops on opposite colors. This was thought to be a draw but the rook and bishop generally win. It takes up to 98 moves (Nunn 2002:342ff).
Read more about this topic: Chess Endgame
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