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.

[Diagram]

White goes first and kills

White can start her 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 approaching a life and death problem the right way.).

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

Black can live

tapir: Black can tenuki twice here. Actually, for white has to surround first before trying to kill.


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


This is a copy of the living page "Two-Space Notchers" at Sensei's Library.
(OC) 2011 the Authors, published under the OpenContent License V1.0.
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