Two-Space Notchers

    Keywords: Life & Death

Two-space notchers are groups that consist of a chain on the second line, interrupted by a notch of two empty spaces on the second line and two to four stones on the third. The term was invented by James Davies. See also Notchers, One-Space Notchers and Three-Space Notchers.


[Diagram]
Two-space notcher  

The rule for two space notchers is, depending on how you want to formulate it, either "Five die, Seven live" or "Six is unsettled". For the time being we'll leave proof of the two extremes to you and demonstrate the unsettled case.

[Diagram]
Black goes first and lives  

If Black goes first, he can live. White is again rather stubborn to keep trying with 2 and 4, but after 5 Black has completely constructed the two eyes he needs to live.

Eggplant86: isn't it better style for B to move black 1 to black 3? I don't see a way for W to kill and it could be better yose.

[Diagram]
White goes first and kills  

White can start his attack with a hane at 1.

(Reducing your opponent's eye space like this should always be the very first option you consider when examining the status of one of his groups, by the way. See also the article on How to approach a life and death problem.).

Even if Black were to resist, White can keep his group dead.

unkx80: See also Two Space Notchers Not Fully Connected.


Classification

[Diagram]
Two-space notchers  

Marked spots: possible weaknesses
Marked stones: legs


Classification...

211

[Diagram]
211WW  
[Diagram]
211WN  
[Diagram]
211WS  
[Diagram]
211NN  
[Diagram]
211NS  
[Diagram]
211SS  

All of the 211xx are dead


212

[Diagram]
212WW  
[Diagram]
212WN  
[Diagram]
212WS  
[Diagram]
212NW  
[Diagram]
212NN  
[Diagram]
212NS  
[Diagram]
212SW  
[Diagram]
212SN  
[Diagram]
212SS  

All of the 212 are dead


222

[Diagram]
222WW  

aka the flying saucer shape. It is dead

[Diagram]
222WN  

Black can live

[Diagram]
222WS  

Black can live

[Diagram]
222NN  

Black can live

[Diagram]
222NS  

Black can live

[Diagram]
222SS  

See 222SSNotcher


All 222 are "Black can live, White can kill" except 222WW, which is dead.


213

[Diagram]
213WW  

dead

[Diagram]
213NW  

Black can live

(...)


All of 213 can make life, except for 213WW which is dead


223

[Diagram]
223WW  

Black can live

[Diagram]
223WN  

Black is alive

(...)


All 223 are alive, except for 223WW, where Black can live and White can kill.

However, 223WSNotcher shows a killing sequence for White.


233

[Diagram]
233WW  

Black is alive

(...)


All 233xx are alive


Table

See table of notchers


Two-Space Notchers last edited by Dieter on September 26, 2023 - 10:40
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