Zugzwang

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This article uses algebraic notation to describe chess moves.

Zugzwang (German for "compulsion to move", IPA: [ˈtsuːk.tsvaŋ]) is a term used in combinatorial game theory and in other types of games (particularly in chess). Zugzwang means that one player is put at a disadvantage because he has to make a move — the player would like to pass and make no move. The fact that the player must make a move means that his position will be significantly weaker than the hypothetical one in which it is his opponent's turn to move. In combinatorial game theory, it means that it directly changes the outcome of the game from a win to a loss. The term is used less precisely in other games.

The term is frequently used in chess, to mean that one player (having the move) has no move that does not worsen their position (Soltis 2003:78). Game theory does not apply directly to chess (Berlekamp, et al. 1982:16) (Elkies 1996:136). Sometimes different chess authors use the term zugzwang in different ways (Flear 2004:11-12). In some literature a reciprocal zugzwang (see below) is called zugzwang and a one-sided zugzwang is called a squeeze (Hooper and Whyld 1992).

In a chess endgame, being in zugzwang usually means going from a drawn position to a loss or a won position to a draw, but it can be from a win to a loss, or a substantial loss of material which probably affects the outcome of the game. A chess position of reciprocal zugzwang or mutual zugzwang is equivalent to the more precise definition of zugzwang in game theory. Opposition is a special kind of zugzwang (Flear 2000:36). Trébuchet is a special type of zugzwang that is discussed below.

Contents 1 Zugzwang in chess 1.1 Examples from actual play 1.1.1 Fischer-Taimanov, 1971, second match game 1.1.2 Fischer-Taimanov, 1971, fourth match game 1.2 Reciprocal zugzwang 1.2.1 Trébuchet 1.3 Mined squares 1.4 Zugzwang required to win 1.5 Zugzwang in the middlegame and complex endgames 2 See also 3 Notes 4 References 5 External links

[edit] Zugzwang in chess

Normally in chess, having tempo is a good thing, since the player with the chance to move has greater power by being able to choose the "best" next move. Zugzwang typically occurs when all the moves available are "bad" moves, dramatically weakening the moving player's position (Müller and Lamprecht 2001:22).

Zugzwang most often occurs in the endgame when the number of pieces, and so the number of possible moves, is reduced, and the exact move chosen is often critical. The first diagram gives a simple example. If it is Black's move, he gets to a lost position (the white king gets to either the c5 or e5 square and wins one or more pawns and can advance his own pawn toward promotion). If it is White's move, there is no zugzwang (Flear 2004:11-12). The squares d4 and d6 are corresponding squares. Whenever the white king is on d4 with White to move, the black king must be on d6 to prevent the advance of the white king. In many cases, the player having the move can put the other player in zugzwang by using triangulation. Zugzwang is very common in king and pawn endgames, where it is frequently achieved through triangulation.

Pieces other than the king can also triangulate to achieve zugzwang — e.g., see the queen versus rook position at Philidor position. Zugzwang is a mainstay of chess compositions and occurs frequently in endgame studies.

[edit] Examples from actual play

Here are some examples of zugzwang from actual games.

[edit] Fischer-Taimanov, 1971, second match game

Some zugzwang positions occurred in the second game of the 1971 candidates match between Bobby Fischer and Mark Taimanov. In the position in the diagram, Black is in zugzwang because he would rather not move, but he must (Wade & O'Connell 1972:413). The game continued:

• 85... Nf3
• 86. h6 Ng5
• 87. Kg6

and Black is again in zugzwang. The game ended shortly (because the pawn will slip through and promote) (Kasparov 2004:385):

• 87... Nf3
• 88. h7 Ne5+
• 89. Kf6 1-0.

[edit] Fischer-Taimanov, 1971, fourth match game

In the position on the right, White has just gotten his king to a6, where it attacks the black pawn on b6, tying down the black king to defending it. White now needs to get his bishop to f7 or e8 to attack the pawn on g6. Play continued:

• 57... Nc8
• 58. Bd5 Ne7
• 59. Bc4! Nc6
• 60. Bf7 Ne7

Now the bishop is able to make a tempo move. It is able to move while still attacking the pawn on g6, and preventing the black king from moving to c6.

• 61. Be8

and Black is in zugzwang. The knight is unable to make a tempo move; moving it would allow the bishop to capture the kingside pawns. The black king must give way.

• 61... Kd8
• 62. Bxg6! Nxg6
• 63. Kxb6 Kd7
• 64. Kxc5

and White has a won position. Either one of White's queenside pawns will promote or the white king will attack and win the black kingside pawns and a kingside pawn will promote. Black resigned seven moves later (Silman 2007:516-17).

[edit] Reciprocal zugzwang

A special case of zugzwang is mutual zugzwang or reciprocal zugzwang, which is a position such that who ever is to move is in zugzwang. An example is shown in the second diagram — if White is to move the game is drawn; if Black is to move he loses (Flear 2004:22). According to John Nunn, positions of reciprocal zugzwang are surprisingly important in the analysis of endgames (Nunn 1999:7).

[edit] Trébuchet

An extreme type of reciprocal zugzwang, called trébuchet is shown in the third diagram. It is also called a full-point mutual zugzwang because a full point (win versus loss) is at stake. Whoever is to move in this position loses the game — they must abandon their own pawn, thus allowing their opponent to capture it and proceed to promote their own pawn (Flear 2004:13).

The second diagram shows a position in which a trébuchet can be reached to win the game. The first king to reach the blocked pawns will win. Play continues:

• 1. Kxh6 Kxc3
• 2. Kg5 Kd3!

2... Kd4?? loses because after 3. Kf5 Black is on the wrong side of the trébuchet.

• 3. Kf5 Kd4!

and Black wins the pawn and the game (see King and pawn versus king) (Silman 2007:98).

Marc Bourzutschky has used computer analysis to find some complicated trébuchet positions. If White is on move, Black quickly drives White's king toward the corner and mates no later than move 8, e.g. 1.Kb2 (1.Nhg7 Qf4+ or 1.Nh4 Qe3+ also leaves White's king in trouble) Qg2+ 2.Kb3 Qb7+! 3.Ka3 Qb6 4.Nf4+ Kc4! 5.Ka2 Qb3+! 6.Ka1 Kb4 7.Ng7 Ka3 8.Nge6 Qb2#. Black on move must give ground, enabling White to gradually improve the positions of his pieces, e.g. 1...Kc4 (1...Kc3 allows 2.Nf2 Qxf2?? 3.Ne4+) 2.Kd2! Kd5 3.Ne3+ Ke5 4.Ng7 and White mates by move 42 according to Bourzutschky.-- scroll down to No. 282

[edit] Mined squares

Mined squares are squares such that a player will fall into zugzwang if he moves onto the square. In the diagram on the right, if either king moves onto the square near it labeled "1", he falls into zugzwang if the other king moves into the mined square near him. These are a type of corresponding squares (Dvoretsky2003:18).

[edit] Zugzwang required to win

In some endgames, zugzwang is required to force a win. These include: rook (and king) versus king checkmate, two bishops versus king checkmate, bishop and knight versus king checkmate, queen versus rook, queen versus knight, queen versus two knights, and queen versus two bishops (Soltis 2003:79).

[edit] Zugzwang in the middlegame and complex endgames

The game Fritz Sämisch – Aron Nimzowitsch, Copenhagen 1923,^[1] is sometimes called the "Immortal Zugzwang game" because the final position is widely accepted as being an extremely rare instance of zugzwang occurring in the middlegame. It ended with White resigning in the position in the diagram.

White has a few pawn moves which do not lose material, but eventually he will have to move one of his pieces. If he plays 1.Rc1 or Rd1 then 1...Re2 traps white's Queen; 1.Kh2 fails to 1...R5f3, also trapping the queen (white cannot play Bxf3 here because the bishop is pinned to the king); 1.g4 runs into 1...R5f3 2.Bxf3? Rh2 mate. 1.a3 is met by 1...a5 2.axb4 axb4 3.b3 Kh8 (waiting) 4.h4 Kg8 and White has run out of waiting moves and must lose material. Other white moves lose material in more obvious ways. Whether the position is true zugzwang is debatable, however, because even if white could pass his move he would still lose, albeit more slowly, after 1...R5f3 2.Bxf3 Rxf3, trapping the queen and thus winning queen and bishop for two rooks (Horowitz 1971:182).

Harper-Zuk, Halloween Open, Burnaby, British Columbia 1971^[2] is a grisly example of zugzwang in the middlegame. White's queen, rook, knight, and king have a total of one legal move (Qh3), and that move loses the queen and then the game (... gxh3 followed by ... Qxg2#). The game concluded: 37.b5 Kh8 37...Nf5 and Nd4-e2 was crushing, but letting White self-destruct is even quicker. 38.a4 Kh7 39.a5 Kg8 0-1 After 40.axb6 axb6, white is forced to play 41.Qh3, and then it's mate in two: gxh3 42.Kh2 Qxg2#.

An unusual example of zugzwang in a complicated endgame occurred in the position at right. On the previous move Black, with a winning position, had played 73...d4? and White responded 74.R(from d2)-d3!!, when Black, a knight up with three dangerous passed pawns, suddenly must fight for a draw. Tim Krabbé explains that the pawns on d4 and e4 are blocked and pinned, the knight is bound to the defense of e4, the rook is bound to the defense of d4, and the pawn on b4 is bound to the defense of the knight. Krabbé analyzes as best for Black 74...b3! 75.Rxd4 Rxd4 76.Rxc3 Rd8 77.Rxb3 Re8 78.Re3 Re5 79.Rc3 (79.Kxf6? Rxa5 82.Kg6 Ra1 83.f6 Rg1+ wins) Re8 80.Re3 Re5 81.Rc3 and the game will end in a draw by repetition of moves. Instead, Black played 74...Nb5? 75.Rxe4 Nd6 76.Re6 Rc6 77.Rxd4 Rxh6+ 78.Kxh6 Nxf5+ 79.Kg6 1-0 ^[3].

[edit] See also

• Opposition (chess)
• Null-move heuristic
• Seki
• Combinatorial game theory, in which all mutual zugzwangs are equivalent to 0.
• Triangulation (chess)
• King and pawn versus king
• Bishop and knight checkmate

[edit] Notes

[edit] References

•  Elwyn R. Berlekamp, John H. Conway, and Richard K. Guy (1982). Winning Ways for your Mathematical Plays (two volumes). Academic Press. ISBN 0-12-091101-9 (vol 1) ISBN 0-12-091102-7 (vol 2).  (A second edition was published by A. K. Peters, in four volumes)

•   Dvoretsky, Mark (2003). Dvoretsky's Endgame Manual. Russell Enterprises. ISBN 1-888690-19-4. 

•  Noam D. Elkies (1996). "On numbers and endgames: combinatorial game theory in chess endgames". Games of No Chance 29: 135-50. 

•  Glenn Flear (2000). Improve Your Endgame Play. Everyman Chess. ISBN 1-85744-246-6. 

•  Glenn Flear (2004). Starting Out: Pawn Endings. Everyman Chess. ISBN 1-85744-362-4. 

•   Hooper, David and Whyld, Kenneth (1992). The Oxford Companion to Chess, 2nd Edition. Oxford University Press. ISBN 0-19-866164-9.  Reprint: (1996) ISBN 0-19-280049-3

•  I. A. Horowitz (1971). All About Chess. Collier Books. 

• Kasparov, Gary (2004), My Great Predecessors, part IV, Everyman Chess, ISBN 1-85744-395-0

•   Karsten Müller and Frank Lamprecht (2001). Fundamental Chess Endings. Gambit Publications. ISBN 1-901983-53-6. 

•  John Nunn (1999). Secrets of Rook Endings. Gambit Publications. ISBN 1-901983-18-8. 

• Silman, Jeremy (2007), Silman's Complete Endgame Course: From Beginner to Master, Siles Press, ISBN 1-890085-10-3

•  Andrew Soltis (2003). Grandmaster Secrets: Endings. Thinkers' Press. ISBN 0-938650-66-1. 

• Wade, Robert & Kevin O'Connell (1972), The Games of Robert J. Fischer, Batsford, ISBN 0-7134-2099-5

[edit] External links

• Fischer-Taimanov 1971