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Miai
Difficulty: Advanced
Keywords: Go term
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. This 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?
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.
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.
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 :
At this stage it is again obvious that, if white plays A, black plays B. So if white plays B first, ...
... 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 in the FusekiThe concept of miai is important in the fuseki as well. Playing situations that contain miai assure one of being able to achieve at least one of two aims regardless of how the opponent chooses to counter your strategy.
In this common fuseki, Black chooses to play against White's position on the left instead of continuing his own development on the right, for example by forming a san ren sei by playing 1 at 'a'. When W answers with the common attachment at 2, B plays the joseki of 3 and 5 and finishes with the high extension at 7. The modern popularity of 7 instead of the alternative play at 'b' is attributed to Takemiya Masaki and is based on a miai strategy. B plays 7 in order to increase the value of a follow up at 'c'. He then considers 'c' and 'a' on the right to be miai and is content to play whichever W does not take for herself.
White chooses to counter B's intentions on the left so B makes his san ren sei on the right side. To play like this B must be willing able to handle the W invasion at 'a'.
Here White decides to prevent a B formation on the right and splits the side with 1. As a result, B is able to follow up on the right by approaching W's lower left corner at 2 and W will probably answer with something like 3. Note that W 1 is also a typical example of miai. The follow up here is for B to play against the White stone with either 'a' or 'b' and for W to reply with an extension in the direction away from the approach stone. Since both directions are open for W (are miai) there is no urgent play on the right side for B at this time. The future course of the game may make one direction or the other more valuable. If that happens the miai situation disappears and the right side will become more urgent. The equivalence of the left and right side is much less clear here than in the examples at the top of this page. There is no simple calculation this early in the fuseki to show that a play on the left and a play on the right have the same value. In professional play that equivalence has to be demonstrated over the board. In the fuseki above there are professional examples of W choosing both the left and the right with no clear advantage from either choice. For the moment, we can consider them miai (until someone comes along with an approach that demonstrates otherwise!). This is a copy of the living page "Miai" at Sensei's Library. (C) the Authors, published under the OpenContent License V1.0. |