Big Eye Wins Semeai

    Keywords: Tactics, Theory

Japanese 大ナカ小ナカ (oonaka - konaka), 大ナカデ小ナカデ (oonakade - konakade)

In a capturing race a big eye (大ナカデ) has an advantage over a small eye (小ナカデ) similar to the advantage a group with an eye has over a group with no eye. See eye versus eye capturing race and Eyes win semeais.

[Diagram]

Seki?

Both groups have an eye and all liberties are internal. This looks a lot like a seki, but Black is dead.[10]

[Diagram]

Playing it out (1)

B2, B4, B6 = pass

[Diagram]

Black is dead

No matter who starts first, white can win the semeai because of his big eye.

The group with the big eye has a big advantage in a semeai. Not only does the big eye confer extra liberties, the big eye gets the shared dame for liberties. The group with a small eye needs more external liberties if he is to have a chance of winning. This is very much like eye vs no eye semeai.


[Diagram]

Bigger eye wins

If both players have big eyes, the one with the bigger eye has the advantage. Here White is dead.

[Diagram]

Playing it out (1)

W2 = pass

[Diagram]

Playing it out (2)



[Diagram]

Playing it out (3)

After B1 White has 4 liberties, Black has 7. White is dead.


[Diagram]

Critical position

This is the critical position in this semeai. Black has 4 obvious liberties. It looks like White has 3 liberties, but big eyes have more liberties, as a rule. The rule of thumb is that the 4-point big eye has 5 liberties. Black has played one, so White has 4 left. Whoever plays first wins.

[Diagram]

Black wins



[Diagram]

Black wins (continued)

Black is plainly one move ahead, now. White is dead.

[Diagram]

White wins



[Diagram]

White wins (continued)

Now White is plainly one move ahead. Black is dead.


[Diagram]

Seki?

We have altered the position by giving the groups one shared dame, [circled point]. Since the groups started with the same number of liberties and each has an eye, is this seki?

Actually, no. The shared dame is a liberty for the big eye, White, so Black is dead.

To show that, Black to play loses and cannot make seki.

[Diagram]

Black loses

Now if Black plays at [circled point] White will take Black's corner stones and Black will lose, so B5 passes.

[Diagram]

Black loses (ii)

B7 passes.

The order of play is important. If White takes Black's stones before almost filling Black's eye, Black can make seki.

[Diagram]

Black loses (iii)

After W10 Black is lost.



[10] tderz: Formula:
Black IL + OL < White's IL + SL
SL = 4 , i.e. both have 4 shared liberties
IL(B) = 3-2 = 1
IL(W) = 5-3 = 2 , hence one more.
The number 5 derives from the sequence (1-2-3-) 5, 8, 12, 17 ... -> (?)


See also:


This is a copy of the living page "Big Eye Wins Semeai" at Sensei's Library.
(OC) 2007 the Authors, published under the OpenContent License V1.0.
[Welcome to Sensei's Library!]
StartingPoints
ReferenceSection
About