Zugzwang

[tsook-tsvahng]

'Zugzwang' is also a musical work by Juan Maria Solare.

Zugzwang (German for "compulsion to move", ) is a term originally used in chess which also applies to various other games. The concept finds its formal definition in combinatorial game theory. It describes a situation where 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 game theory, it specifically means that it directly changes the outcome of the game from a win to a loss. The term is used less precisely in games such as chess; e.g., the game theory definition is not necessarily used in chess , . For instance, it may be defined loosely, as "a player to move cannot do anything without making an important concession" . Zugzwang is a common technique to help the superior side win a game and sometimes it is necessary to make the win possible .

The term zugzwang is frequently used in chess. A player whose turn it is to move who has no move that does not worsen their position is said to be in zugzwang . Thus every move would make their position worse, and they would be better off if they could pass and not move. Sometimes different chess authors use the term zugzwang in different ways . In some literature a reciprocal zugzwang (see below) is called zugzwang and a one-sided zugzwang is called a squeeze . The term was first used by Emanuel Lasker in 1905 .

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 . Trébuchet is a special type of zugzwang that is discussed below.

Positions with zugzwang occur fairly often in chess endgames. For instance, twelve of the 105 endgames in the book Endgame Virtuoso Anatoly Karpov involve zugzwang . According to John Nunn, positions of reciprocal zugzwang (see below) are surprisingly important in the analysis of endgames , .

The remainder of this article is about zugzwang in chess.

Introduction

There are three types of chess positions:

both sides would benefit if it were their turn to move
only one player would be at a disadvantage if it were his turn to move
both players would be at a disadvantage if it were their turn to move.

The great majority of positions are of the first type. In chess literature, most writers call positions of the second type zugzwang, and the third type reciprocal zugzwang or mutual zugzwang. Some writers call the second type a squeeze and the third type zugzwang , .

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, tangibly weakening the moving player's position (usually from a draw to a loss or from a win to a draw) .

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 diagram on the right 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 the king must retreat and Black is out of danger . 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; that article has in illustrative example. 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.

Examples from games

Fischer versus 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: a king move would lose the knight, while a knight move would allow the passed pawn to advance . 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) :

87... Nf3

88. h7 Ne5+

89. Kf6 1-0.

Fischer versus 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. Knights are unable to make a tempo move , so moving the knight 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 , , .

Tseshkovsky versus Flear, 1988

This position from a 1988 game between Vitaly Tseshkovsky and Glenn Flear shows an instance of "zugzwang" where the obligation to move makes the defense more difficult but it doesn't mean the loss of the game. A draw by agreement was reached eleven moves later .

Reciprocal zugzwang

A special case of zugzwang is reciprocal zugzwang or mutual zugzwang, which is a position such that who ever is to move is in zugzwang. Positions of reciprocal zugzwang are surprisingly important in the analysis of endgames , .

The diagram on the right shows a position of reciprocal zugzwang. If Black is to move, he must move 1... Kd7 and lose because White will move 2. Kb7, promote the pawn, and win. If White is to move, he must either abandon protecting the pawn (any move other than 1. Kc6), or move 1. Kc6, which is also a draw because it stalemates Black. Both sides are in zugzwang, so it is a reciprocal zugzwang , .

In a position with reciprocal zugzwang, only the player to move is actually in zugzwang. However, the player who is not in zugzwang must play carefully because one inaccurate move can cause him to be put in zugzwang .

Second example

Another example is shown in the diagram on the right—if White is to move the game is drawn; if Black is to move he loses .

With White to move:

1. Kd5 Kd7

2. c5 Kc7

3. c6 Kc8!

4. Kd6 Kd8!

Black has the opposition and draws because 5. c7+ Kc8 6. Kc6 is stalemate.

If Black is to move, White wins

1. ... Kd7

2. Kb6 Kc8

3. Kc6 Kd8

and White wins with

4. c5

4. Kb7.

Example from play

The position at right is a position that could have occurred in the 1961 game between Viacheslav Kalashnikov and Anatoly Karpov. White to move in this position draws, but Black to move loses. Karpov's 49th move in the actual game avoided the zugzwang and the game was drawn . This is one of 209 mutual zugzwang positions in the rook and pawn versus rook endgame .

Example in study

This position is a mutual zugzwang from a 1792 study. The first player to move runs out of moves and loses .

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 .

Example

This 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 endgame) .

Analysis from actual game

In this analysis from a 1978 game between Miguel Najdorf and Henrique Mecking, whoever is to move loses. (It would have been White's move had the analysis position occurred in the game.)

In endgame study

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

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 marked with the dot of the same color, he falls into zugzwang if the other king moves into the mined square near him. These are a type of corresponding squares .

Zugzwang required to win

In some endgames, placing the opponent in zugzwang is required to force a win. These include:

rook (and king) versus king checkmate
two bishops versus king checkmate
two knights versus pawn checkmate
Bishop and knight checkmate
queen versus rook
queen versus knight
queen versus two knights, and
queen versus two bishops .

In addition, zugzwang is required in many King and pawn versus king endings in order to force promotion of the pawn . (See pawnless chess endgames and fortress (chess) for some discussion of some of these endings.)

Zugzwang helps the defense

Zugzwang usually works in favor of the stronger side, but sometimes it aids the defense. In this position based on a game between Zoltán Varga and Peter Acs, it saves the game for the defense:

1... Kc4!! Reciprocal zugzwang

2. Nc3 Kb4 Reciprocal zugzwang again

3. Kd3 Bg7 Reciprocal zugzwang again

4. Kc2 Bb6

5. Kd3 Bg7

'''6. Nd5+ Kxa4

7. Ke4 Kb5

8. Kf5 Kc5

9. Kg6 Bd4

10. Nf4 Kd6

11. h6 Ke7

12. h7 Bb2 ½-½ .

Zugzwang in the middlegame and complex endgames

Sämisch versus Nimzowitsch

The game Fritz Sämisch versus Aron Nimzowitsch, Copenhagen 1923, is known as the "Immortal Zugzwang Game" because some consider the final position to be 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 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 . Harry Golombek states that it is a misnomer to call this a true zugzwang position . Black would win even without the zugzwang .

Harper versus Zuk

Harper-Zuk, Halloween Open, Burnaby, British Columbia 1971 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#.

Dongen versus Wijsman

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.Rd2-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 .

Zhilin versus Chernov

In the game between Vitaly Valentinovich Zhilin and Chernov (or Tchernov), White was a pawn down and just sacrificed a bishop on h3. After 1. Kh4! Black is placed in zugzwang after moving his b- and h-pawns. The game continued:

1. Kh4! b6

2. Kh5 b5

3. Kh4 h5

4. Kxh5

Now Black is in zugzwang and resigned , .

Fischer versus Rossetto

In this 1959 game between future World Champion Bobby Fischer and Héctor Rossetto, 33. Bb3! effectively puts Black in zugzwang. If Black moves the king or rook, it allows White to move Rb8 and knight moves by Black allow White to move Be6. (If Black makes any king move then White moves Rb8 and then either Black exchanges rooks and the pawn promotes, or the rook captures the pawn and White wins the knight. If Black moves ...Ra8 or ...Re8 then Rb8 supports the pawn to promote. If Black moves the knight then Be6 attacks the black rook and supports the pawn's promotion square.) That leaves only pawn moves, and they quickly run out. Black made four pawn moves, White responded with pawn moves, and then Black resigned .

Quotes

"Zugzwang is like getting trapped on a safety island in the middle of a highway when a thunderstorm starts. You don't want to move but you have to." - Arthur Bisguier