Countering mirror go

  Difficulty: Intermediate   Keywords: Opening, Strategy

Mirror go played by White can be countered by Black playing on the tengen, although this is not necessarily the best way. Below are several examples of countering mirror go. The result is often absurd, but if the player who is mimicking aborts halfway, the other player would have succeeded in stopping the mirror go.

The more challenging task is to do so without giving your opponent any opportunity to take advantage of your mirror defense attempt (by suddenly responding with a better move than yours).

Table of contents Table of diagrams
Tengen damezumari (1)
Tengen damezumari (2)
Setting up ladders (1)
Setting up ladders (2)
Setting up ladders (3)
Setting up ladders (4)
Setting up ladders (5)
Setting up a superko in manego
Not necessarily mirror go
Beware of bad anti-strategies
Proper strategy?

1. Shortage of liberties due to tengen

The opponent stone at tengen can be used to create shortage of liberties.

[Diagram]
Tengen damezumari (1)  
[Diagram]
Tengen damezumari (2)  

[1]

What's the best continuation if B7 connects at 8?


2. Setting up two ladders

If no opponent stone at tengen is available to create shortage of liberties, then setting up two ladders is another technique.

[Diagram]
Setting up ladders (1)  
[Diagram]
Setting up ladders (2)  
[Diagram]
Setting up ladders (3)  
[Diagram]
Setting up ladders (4)  
[Diagram]
Setting up ladders (5)  



Incidentally, this very technique is seen in a professional game: Hosai Masao - Two Ladders Mirror Go.


3. Setting up two kos

Here's another standard anti-mane-go strategy that can be used instead. It assumes that some form of superko rule is in force. White starts by creating two kos; call these kos A and B, and their mirror images A' and B'. White captures in A, and Black mimics by capturing in A'. Then White captures in B, and Black captures in B'. Then White recaptures in A', and Black recaptures in A. Then White recaptures in B'. The superko rule forbids Black from recapturing in B, so he has to stop mimicking.

[Diagram]
Setting up a superko in manego  

4. More strategic considerations

[Diagram]
Not necessarily mirror go  

Not everything that looks like it, is actually mirror go. In a database search, there are nine pro games with this exact position. White won eight out of nine, and seven of those were without komi. Since 1985, the pros seems to have decided that this is not a viable strategy for black. (If you delete B1 from the board and look at it as black to play, it's quite a common position--and people don't often play tengen here.)

[Diagram]
Beware of bad anti-strategies  

It would be a mistake is to play an irrational move in an attempt to capture black in a cheap trick. In Example 2, white notices black's mirror go when black plays B9. White plays W10 in an attempt to begin a capturing race in which B1 is a burden to black. However, when black breaks mirror go by extending to a. Ladder strategies may share of the same bad taste.

One may still feel this is playable for White.

[Diagram]
Proper strategy?  

Proper strategy is to recognize the possibility of mirror go from the start and play a solid territorial game in which black's tengen stone feels inconsistent and does not aid black in fighting or building a moyo. In Example 3, white plays a solid territorial game that would feel like relying on komi even if black were not playing manego. While B9 is a natural move, B1 makes W8 feel like a light refutation of ippoji. Black has played a territorial game that is inconsistent with his first move and has lost most of its advantage.

xela: What if white plays W2 and then black decides not to play mirror go? Many people would prefer to have W2 on the 4-4 or 4-5 point.


5. Real life examples

[1] The Countering (1) example appears in Akira's game against Okamura in Hikaru no Go chapters 14-15.


Countering mirror go last edited by 202.156.180.188 on September 9, 2013 - 18:48
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