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Miai
  Difficulty: Advanced   Keywords: Go term

[Diagram]
Diag.: Miai

The term 'Mi-ai' denotes that a player has two different options to his or her disposal. For example, in this diagram white lives because if black plays at A, white plays at B, and if black plays at B, white plays at A, in both cases making two eyes. We say that A and B are 'mi-ai for two eyes'. In general any such situation where when one player takes or prevents one of two options, the opponent will play the other, is called mi-ai. This might be the case in a local position like this, but also in more general, strategic concepts. For example, if black has a large moyo which white can reduce or invade from two sides, the two invasions might be mi-ai.

Sometimes, the english term equivalent is used for this concept, although it is a simplification of the meaning.



BillSpight: Equivalence is an important aspect of miai. The above is a better example of sente than miai. Each player prefers b to a. In some miai, one player prefers one point while the other player prefers the other. For a good example of miai, see wariuchi.
Also, there is generally a strong expectation with miai that if one player takes one miai point, the other player will take the other. In this example, if White plays at b, we do not expect that Black will play at a -- or vice versa, for that matter ;-).
How about this for an example?

[Diagram]
Diag.: Miai


It is better not to play in miai points without additional reason. For example in the situation above Black move at b is Sente and is worth 2 points. But playing it in the middle game is a loss of a KoThreat which might prove to be decisive for the outcome of the game. -- HolIgor


Miai is not only an observation, something nice-to-know. Miai can be an effective tool when looking for a move.

[Diagram]
Diag.: Miai

This diagram comes from KanazawaProblemOne. When white - mistakenly - plays 1, she makes an eye at the circled points. It is obvious that she can make a second eye at A if she would be able to play at 2. So black plays at 2 in order to prevent that. This is quite an obvious move for black.


[Diagram]
Diag.: Miai

If white plays - mistakenly - at 1 here, the right spot for black to kill her does not jump to the eye as easily as in the previous diagram. All of A, B, C and D deserve several seconds of thought ... unless one thinks of the concept of miai .

If we think of the previous diagram - where White D was answered by Black 1 - we might assume 1 and D to be miai, and answer white 1 with black D :


[Diagram]
Diag.: Miai

At this stage it is again obvious that, if white plays A, black plays B. So if white plays B first, ...


[Diagram]
Diag.: Miai

... black answers at 4 - again using miai reasoning. The shape is a BentFourInTheCorner and white is dead.



One cannot assume thoughtlessly that two moves are miai, but doing so can lead to the right move, and reduce the amount of thinking over a problem.

--Dieter


Miai is indeed great for players with poor reading abilities like me :o) I don't know if creating miai points in local positions can be considered as a (nameless) tesuji, but here is a small example I've found in a chinese tsumego book :

[Diagram]
Diag.: Black's best move ?

The goal for B is to separate white stones. Obviously, this would generate a big profit for B (territory in the corner and prisoners). How ?


[Diagram]
Diag.: Double miai

B 1 is the suji making respectively miai of A and B for connecting the marked stone to the upper black group, and miai of C and D for cutting.

Of course, just like the example at the top of this page, these points aren't strictly equivalent, since both players now want A and C in order to minimize loss/maximize profit. But IMHO, this keeps being a detail compared to the change in the local status.


Granted, this example doesn't add very much to the topic, but it shows the use of miai for attacking in a not so basic position. So I thought it might be useful :-)

--Nando


See also Miai in the Fuseki

(Topic moved to its own page) --DaveSigaty



This is a copy of the living page "Miai" at Sensei's Library.
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